OK, so the artificer is the most complicated class in the game and you probably don’t want to play it. The wizard is definitely complicated, and with the right tack can do the things you’re interested in, but it’s possibly overpowered plus doesn’t really seem to have the imagery you want out of the box.
Enter the Beguiler
The beguiler from Player’s Handbook II is not as complicated as the wizard. Rather than maintaining an ever-expanding spellbook and preparing spells every morning, the beguiler just knows every spell on his spell list, and can use them in any combination he likes provided he’s still got spell slots left for the day. And ultimately, the beguiler’s not nearly as powerful.
On the other hand, the beguiler is far more obviously stealth-oriented. They have Hide and Move Silently as class skills, they can wear light armor, and they get bonuses for surprising people with their spells. Their spell list is quite good, with lots of different options, including an incredibly flexible array of illusions.1 Their 6+Int skills mean they are quite likely to have solid mundane skills for sneaking about and slipping into places they shouldn’t be.
I recommend considering the Master of Poisons and Poison Spell feats (both from Drow of the Underdark) to excel with poisons. I recommend against actually playing a drow, though, master poisoners though they are, because the LA +2 is very, very bad.
Also, the mindbender prestige class from Complete Arcane, though generally quite poor, is an amazing choice for a beguiler to take for a single level at 6th (i.e. 5th-level beguiler/1st-level mindbender). The entry is easy, and mindbender improves your spellcasting while giving you telepathy out to 100 ft., which qualifies you for the excellent Mindsight feat (Lords of Madness). Now you know exactly where every thinking mind in 100 ft. is, and that’s awesome. Continue taking beguiler levels thereafter (i.e. 5th-level beguiler/1st-level mindbender/beguiler +x)
- Just how flexible and useful illusions are does depend a fair bit on the DM, so you should ask about that before making a character focused on them, but in my experience most DMs are willing to let them go pretty far.
Double Jeopardy
OK, so maybe the beguiler sounds pretty cool and all, but you actually liked the way that wizard was sounding. No problem: the ultimate magus prestige class from Complete Mage is an excellent option, and nothing works so well for it as the beguiler does. Start out as a 1st-level beguiler for the sweet, sweet 4×(6+Int) skill points, and then multiclass into wizard for three levels in order to qualify for ultimate magus. Ultimate magus will improve both beguiler and wizard spellcasting. Make sure to take Practiced Spellcaster (beguiler) before you start; Practiced Spellcaster is also from Complete Mage. Being an illumian and taking the Power Sigil (Krau) feat, both from Races of Destiny, is also highly recommended.
In this approach, being a specialist wizard banning Enchantment and Illusion is a good idea because beguiler is very strong in both of those schools, so you won’t miss those spells as much. Conjuration or Transmutation are probably your best bets for specialty, though really anything can work. Practiced Spellcaster (beguiler) is a must and Power Sigil (Krau) is highly recommended, but aside from that you can still take Master of Poisons and Poison Spell. If you are a human subrace—and illumians are—, also consider Able Learner to allow you to more easily maintain your ranks in Hide and Move Silently.
Classes
Five classes stand out to me as ideal choices for entry to warshaper.
Pugilist Fighter
Pugilist is a variant fighter from Dragon vol. 310. It gains Improved Unarmed Strike, slightly increased unarmed strike damage (but it doesn’t scale like the monk’s), the Endurance feat, and then one other feat (or special “Pugilist ability”) of your choice from a decent-size list (comparable to the size of the core fighter bonus feat list, but much smaller when you consider all of the supplement feats that a fighter can usually take). It’s kind of solid for all the feats you get in one level, but I’d definitely not take more than the one.
Pugilists give up martial weapon proficiency, but retain all armor proficiencies.
Knight
Knight gets d12 HD, heavy armor, and Bulwark of Defense and Test of Mettle in the first four levels. You also get the Fighting Challenge, which is OK, and Mounted Combat, which... is maybe useful? Anyway, the first four levels are pretty good (in fact, it is often claimed that knight has five good levels: 1, 2, 3, 4, and 20).
I would only go with knight if I got at least three levels; Bulwark of Defense is a really nice feature. I’d want Test of Mettle if my Charisma was good, but a level of pugilist or crusader could fit in well.
The big problem with knight is the Knight’s Code, which is possibly even stricter than the paladin’s (though the penalty is less severe). It also demands that you remain lawful: that makes it hard to also take a level of barbarian, and you want a level of barbarian, because...
Barbarian
Barbarians can get Improved Unarmed Strike as a bonus feat, but it’s not worth it to do so. Instead, you want a level of barbarian for relevant stat bonuses, d12 HD, and most importantly, the lion spiritual totem from Complete Champion. Pounce gives you absolutely critical mobility.
Warblade
Warblade gets medium armor proficiency, not heavy, but also gets d12 HD, and a number of really useful maneuvers. Tiger Claw can let you attack more often, which is nice, with wolf fang strike and sudden leap.
Crusader
Doesn’t get Tiger Claw like warblade does, and only a d10 HD, but it does get heavy armor proficiency, and more importantly, Devoted Spirit is solid, reliable non-magical healing. Crusaders are the best in-combat healers in the game, while remaining solid martial forces in their own right. Plus Steely Resolve can dramatically improve your ability to remain standing.
Crusader 4 itself could be a solid entry to warshaper, though I’d probably go with levels of barbarian and pugilist first.
Feats
Superior Unarmed Strike
This feat from Tome of Battle gives you a scaling unarmed strike damage similar to (slower than) the monk, if you care. It’s decent enough, particularly when you’re getting size bonuses.
Improved Natural Attack (unarmed strike)
It’s a damage boost that stacks with everything; might as well.
Note that in theory you could replace this with a fanged ring if you were in a game where you could expect to get a 10,000 gp magic item any time soon, but you aren’t
Stone Power
Another feat from Tome of Battle, this allows you to take attack penalties (similar to Combat Expertise, no larger than your BAB or 5, whichever is less), gaining a number of temporary hit points equal to twice the penalty. The temporary hit points last 1 round, but you can continuously add up to 10 HP that basically “doesn’t count” as damage you take ever round. At low levels, that removes a lot of damage.
Suggestion
Barbarian 1/Pugilist 1/Crusader 2
Heavy armor, a d12 HD and three d10s. Rage and pounce from barbarian, Improved Unarmed Strike, Endurance, and another feat of choice from pugilist, Steely Resolve, Furious Counterstrike, and Indomitable Soul, along with a bunch of maneuvers, from crusader.
For maneuvers, you get five 1st-level maneuvers, a 1st-level stance, and one 2nd-level maneuver. The crusader awkwardly only has only six 1st-level maneuvers to pick from, and leading the attack and vanguard strike are very-nearly identical anyway, so your choices in 1st-level maneuvers don’t matter that much. Anyway, vanguard strike is slightly better than leading the attack, and you don’t need both, so I’ leave out leading the attack and get the other five. For stance, martial spirit and iron guard’s glare pretty much are your best options; the former gives you more healing, while the latter draws attacks towards you by improving allies’ AC without improving yours. The 2nd-level maneuver basically should be mountain hammer, hands down.
For feats, Improved Natural Attack (unarmed strike) and Stone Power are my picks. From pugilist, probably Improved Initiative, since the list is pretty weak; Two-Weapon Fighting or Combat Expertise might be worthwhile if you want to go the TWF route or the tripping route. I’d probably get Superior Unarmed Strike at 6th (unless going for Improved Trip), and Snap Kick (also Tome of Battle) at 9th.
Best Answer
Reflavor an existing class instead
I'd like to suggest a major change to how you approach this problem. Rather than saying you want high INT and no magic, here's the process I'd take:
Here's why - as discussed, there aren't really any existing classes that rely on intelligence without any magical effects. That's not how the world of DnD typically works. Characters are largely either good at fighting or good at magic.
Developing a vision
Focusing on being smart doesn't give a clear vision of what you want your character to do. I'm guessing you don't want to play Stephen Hawking, but he fits all of the criteria you've given us (high INT, no magic). Before you can build a character, it's essential to formulate an idea of how your intelligence would actually manifest in combat & non-combat actions. I can think of a few examples of how that might look:
There are plenty of other ways you could take an intelligent character, but I'd say that before you can build anything you need a clear vision of how your character will play. It's nigh impossible to build a character off of "high int stat, no magic". It's very possible to come up with a reasonable sherlock holmes, or steampunk engineer, or whatever other playstyle you are looking for.
Building a character from that vision
For each of the archetypes I listed above, I'm confident you could get the effect you need either with some creative use of a martial class, or re-flavoring of a magic class. There are several different viable ways you could build each of those characters, with different strengths and weaknesses.
The key principle here is that it's almost universally easier to re-flavor an existing class (potentially with a few tweaks) than it is to create a whole new playstyle. Most DMs are okay with re-flavoring as long as it's not widely off-base for the world their building. Re-flavoring removes concerns of class balance, because you're using a class that is already accepted as balanced.
I'll provide one example to illustrate the point. You could play a bard (any college) to get a battle-commander, mentalist, or saboteur playstyle. Reflavor bardic inspiration to giving commands/advice to your allies, spotting weak spots in your enemies, distracting your enemies, etc. Song of rest becomes skilled first-aid care. The expertise, jack of all trades, and lots of proficiencies are a great match with your encyclopedic knowledge of everything. Countercharm becomes counter-hypnosis.
You can still use many bard spells and re-flavor them as non-magical effects. For example, Suggestion is now powered by hypnosis. Faerie Fire becomes phosphorous powder. Tongues is just a genius-level grasp of language. This could be especially effective if you focus on enchantment-type spells. Some spells wouldn't work, but there are lots of spells that can be re-flavored for the same effect. As long as you follow all of the rules and limitations of magic, this won't cause any balance problems.
This gives you a cohesive, balanced class with a distinctly non-magic playstyle. You're still useful to the party and have plenty of options, but you fit within the rules and don't require a whole host of homebrew or special exceptions. I'm confident that you could do something similar with any of the other playstyles that I listed above, or just about anything you can come up with. Re-flavoring existing classes without changing balance is one of my favorite things to do in DnD.