Order of the Stick only references the actual rules tangentially

First of all, that joke relies on the rules of Order of the Stick being slightly different from those in both 3.5 and Pathfinder: in the actual rules, you cannot provoke an Attack of Opportunity from a given enemy more than once per action, so after you first leave an opponent’s threatened square and provoke an Attack of Opportunity from him or her, you are free to continue moving without provoking again for that movement.

Rich Burlew has stated repeatedly that he sticks to the actual rules only when he thinks it’s funny to do so, or it advances the plot.

Dungeons & Dragons 3.5 options

Nonetheless, similar tactics do work, and in 3.5 at least, the Spiked Chain is a pretty good weapon for it (the feat cost hurts quite a lot though). The typical approach is to use a Reach weapon that can Trip (Guisarme or Spiked Chain are the typical choices), take Combat Reflexes and Improved Trip, and trip anyone who tries to move around you too much. This is one of the most effective tactics available to most mundane warriors in 3.5.

Feats

Combat Reflexes and Improved Trip, as already mentioned, are key here.

Exotic Weapon Proficiency (Spiked Chain) is a pretty good feat here since you can threaten adjacent squares, but you can also use Spiked Gauntlets, Armor Spikes, and so on with a Guisarme to accomplish similar results. Depends whether or not you have room for another feat.

The Stand Still feat is also quite good for this kind of build, and Knock-Down is also pretty good. Stand Still gives you a good option against those you cannot trip for whatever reason, and Knock-Down effectively doubles your damage against those you can. If you have Tome of Battle, Evasive Reflexes brings you quite a bit closer to how the Order of the Stick character actually works, since it allows you to move back instead of taking an Attack of Opportunity (and it doesn’t count as taking your Attack of Opportunity, which means you still can and he still provokes if he moves forward – you still are only going to get to make one AoO per movement action, though).

Races

Strength or Dexterity bonuses are good, Bonus Feats are great, and Large size is awesome but usually over-priced. I’d probably go with Human (or a Human variant that still gets the Bonus Feat, like Azurin or Silverbrow or whatever), Orc (ideally Water Orc), or a Goliath from Races of Stone for Powerful Build and the possibility of gaining true Large size from Mountain Rage (see below). Half-minotaur is very good template here, also netting you Large size, though like Goliath the LA hurts.

Note that if you do not get Improved Trip as a bonus feat (see Wolf Totem Barbarian, below), you’ll need Int 13 to get Combat Expertise. Note that if you go for a Psychic Warrior or War Mind build, you’ll want some Wisdom.

Specific classes

Barbarian 2 with the Wolf Totem is a great start for such a tripper: you get Improved Trip without taking Combat Expertise, which is great. Rage is useful since Strength covers your Trip checks, and you could switch to Ferocity to get a Dexterity bonus (read: more Attacks of Opportunity) instead of a Constitution bonus. The Lion Spirit Totem alternate class feature from Complete Champion gets you Pounce, which is a great option for any melee build (though it does not directly improve your Trip-lockdown ability).

If you are a Goliath (Races of Stone), you could instead take Mountain Rage, which makes you Large for the duration of your Rage: this is excellent for a Trip-lockdown build.

Also look into the Knockback feat, also from Races of Stone, and consider combining it with Fighter 6 using the Dungeoncrasher ACF from Dungeonscape: you’ll broaden your abilities to do both Bull Rush and Trip. So Barbarian 2/Fighter 6 is not bad for a pretty simple build that has a few options. A couple of levels of Fighter are pretty common for such a character just because you do want a lot of Fighter feats. Don’t take too many, though; after you get your core feats, additional feats frequently matter less and less and you want to get real class features.

You will also want to increase your size as much as you can. Trips involve Touch attacks, which means BAB is not super-important to you: consider levels in Psychic Warrior to get the excellent expansion, not to mention being a fantastic alternative to Fighter for Bonus Feats. The War Mind prestige class is also pretty good for this. Cleric is a great dip in general, and can also get you righteous might, a pretty good size increase. Note that you have to be careful about when you Rage if you are a Barbarian and a spellcaster or manifester.

Pathfinder options

In Pathfinder, you can still do it, but not with a Spiked Chain, and you need two feats to do what Improved Trip used to do for one, and you’ll burn through your Attacks of Opportunity twice as fast. In short, Paizo decided that one of the few functional mundane tactics in 3.5 was somehow “too good” and nerfed the hell out of it. They also decided that “just because it costs a feat to use” is not a sufficient reason for an exotic weapon to be be better than a martial one, in one of their most derided and bone-headed fiascoes to date, and thus made the Spiked Chain now pretty much useless and in no way worth a feat. It was only barely worth a feat in 3.5.

Being Large would have helped the Pathfinder Spiked Chain situation somewhat since you’d get Reach that way, but it’s still much better off with a Reach weapon than with a non-Reach weapon even when Large, and more importantly there’s still nothing about the Spiked Chain that actually makes it worthwhile. So use a Guisarme or Heavy Flail instead of a Spiked Chain, and still try to increase your size.

Pathfinder also has Stand Still; it’s slightly different (Combat Maneuver check instead of attack plus Reflex Save), but the two are probably close to equal in usefulness. I’m not sure if there are any Pathfinder feats that serve as stand-ins for Knock-Down or Evasive Reflexes, though.

Duskblade 13/Crusader 1/Jade Phoenix Mage 6 seems to me to be much superior to Duskblade 20. You hit the really big duskblade class feature and retain your highest-level spells.

The issue is timing. The best levels to take Crusader are 5th, 9th, or 13th. Coincidentally, however, 5th, 9th, and 13th are also the levels where it is most painful to have a single level of crusader rather than being a single-classed duskblade, as those are the levels at which you get new levels of spells (and full-attack arcane channeling, in the case of 13th). You have two competing goals: get the next spell level (and full-attack arcane channeling) as soon as possible, while having maneuvers for as long as possible, since they are useful.

Therefore, I recommend taking the crusader level at 6th, 10th, or 14th; that is, I’d take the next spell level first, rather than the maneuvers. Here’s a breakdown of each option:

Duskblade 5/Crusader 1

You can take 2nd-level maneuvers with your first five maneuvers. This means, primarily, that you will have mountain hammer for the longest possible time, which is awesome. Other than that, though, you’ll probably still take a number of 1st-level maneuvers.

Duskblade 9/Crusader 1

You can take 3rd-level maneuvers and stances with your initial set; you can skip crusader’s strike for revitalizing strike, you can still take mountain hammer, and the amazing white raven tactics is available to you. Thicket of blades opens up as an interesting stance option; martial spirit is pretty small at these levels, and thicket of blades greatly improves your presence on the battlefield.

Duskblade 13/Crusader 1

Clearly if you haven’t taken crusader by this point, you should. Duskblade has little to offer, so you lose almost nothing at this point. The disadvantage of waiting this long is that you haven’t had maneuvers at all until this point. The advantage, on top of duskblade features ASAP, is divine surge, an excellent offensive maneuver.

The Awkward Bit

OK, so now that we’ve covered how to do it, there’s one other thing to consider: you cannot use arcane channeling and a martial strike at the same time. Arcane channeling requires a standard action attack or a full-attack, so the attack(s) you get from a strike don’t count. This makes strikes massively less useful to you than they would be to others. A boost or counter heavy selection of maneuvers solves this issue; you could do pretty well with defensive rebuke, shield block, and white raven tactics. But missing out on fantastic options like mountain hammer, tactical strike, the various healing strikes, and divine surge is a disappointment.

It also means you don’t have especially great mobility. You have invested 13 levels in duskblade to allow you to full-attack with spells, so you really do want to be making full-attacks. Crusader doesn’t help with that. Swordsage or warblade would help a little, since Tiger Claw is pretty good at that (sudden leap, arguably pouncing charge), but cleric for Travel Devotion or barbarian for Lion Spirit Totem (Pounce) might be better. Those options don’t lead into a great prestige class like jade phoenix mage, but they still might be better options.

The Other Thing

Finally, item-based healing is generally sufficient in 3.5. In-combat healing is rarely an optimal strategy, barring emergencies; the crusader is far better at this than other classes, but you shouldn’t usually need it. The aura you describe all-but-eliminates the worst emergencies, too. Wands and healing belts are quite sufficient for out-of-combat healing. As Jeor Mattan mentioned in comments, the real draw of actually having a cleric is the various options he or she would provide for removing status conditions, since items have HP-healing pretty much covered (and until you get heal, clerics’ HP-healing spells are pretty poor), and crusaders don’t cover that at all.

This is another situation where a level of cleric may be more useful to you: it would allow you to use wands of any cleric spells you like, with no Use Magic Device check. That will cover a lot your needs.