To answer the question rules-as-written:
Wherever the DM thinks appropriate. There appears to be no answer beyond that (especially nothing as specific as a table of default destinations) using official 3.5e materials - 3PP d20 material or earlier editions may be another matter.
For a more useful answer, we need to go beyond rules-as-written (which after all is the whole point of having a DM in the first place.) The best answer therefore depends on the style of game being played, of which there's infinite variation but here's a few ideas:
The narrative answer:
Wherever adds a good story twist, which probably means a populated area with NPCs to interact with. If it's the PCs first visit to that plane, a large city would probably be a good way to introduce them to the plane, as well as providing a useful home base. On the other hand, a small settlement would provide for more intimate interaction with local NPCs and lead to easier story hooks.
The conjectural cosmological physics answer:
The 3.5e Planar Handbook (p151) mentions planar breaches between planes, where the dividing line between two planes has worn thin. It follows that this would be a likely entry point to another plane, as the barrier between the two would provide the least resistance at these points. Planar material could be flowing in or out of this breach depending on the relative density of the planes concerned.
The Hollywood movie answer:
As mentioned in the opening question, there may well be a specific location on the destination plane that is related somehow to the point of origin of the travelers. Travelers from the plane of water may arrive in the middle of a lake or ocean, for example, while those coming from the plane of fire may arrive in a volcanic area.
To the best of my knowledge, there's no definitive list of these, and in many cases it's necessary to tweak the idea to something that would be appropriate on the destination plane - arrival from Mechanus may seem difficult to do if the destination doesn't have clockwork, but a ring of standing stones shaped like cogs feels like a good fit.
The random chance answer:
The DM grabs whatever maps or charts they have of the destination plane (sketching something out if necessary), makes up a grid reference scheme if needed, and rolls dice. Having a few easily adaptable generic maps at hand (with some locations that can easily be tailored to any plane) can be useful here. Tables would work equally well if preferred.
The murderhobo answer:
The PCs arrive at the entrance to the lair of planar monsters that need to be killed, because... they're not currently dead enough, and they have valuable stuff to take.
The "Teach them a lesson"/"My players are masochists" answer:
(Thanks to Zachiel for - unintentionally - reminding me to include this)
They arrive in the worst possible location. Covered in flames on the Plane of Fire, drowning on the Plane of Water, inside solid rock on the Plane of Earth, between two rotating cogs on Mechanus, five thousand feet above one of Arcadia's layers, etc. You'll probably never run into the problem of unspecified destinations ever again...
There are a lot of ways to make a creature undead.
- Animate Dead: Only works on humanoids.
- Create Undead: Only works on humanoids.
- Finger of Death: Works on everything, but will only turn humanoids into undead.
- The Death Tyrant's Negative Energy Cone: Works on everything, but will only turn humanoids into undead.
- The Shadow Dragon's Shadow Breath: Works on everything, but will only turn humanoids into undead.
- The Shadow's Strength Drain: Works on everything, but will only turn humanoids into undead.
- The Vampire's Bite: Works on everything, but will only turn humanoids into undead.
- The Wight's Life Drain: Works on everything, but will only turn humanoids into undead.
- The Wraith's Create Specter: Only works on humanoids.
None of these methods will create a non-humanoid undead. However, as @keithcurtis points out, the Monster Manual includes a large number of undead that aren't made from humanoid creatures.
- Beholder Zombie
- Bone Naga
- Death Tyrant
- Dracolich
- Minotaur Skeleton
- Ogre Zombie
- Warhorse Skeleton
So clearly it is possible to have non-humanoid undead. So why are there no published methods to make one? Well, I have no proof, but I believe it's to ensure that players can only make undead using the standard statblocks. If, for example, Animate Dead worked on the corpse of any creature, there would either need to be zombie and skeleton statblocks for every creature, or some sort of standardized process for zombifying creatures. The first is pretty clearly unfeasible, and the second tends to be open to exploitation.
That's everything players have access to. However, for DMs, there is a large section on Creating Monsters in the DMG (page 273), including creating monsters by modifying existing monsters. For a Vampire Pixie, I'd recommend starting by applying the changes listed in the Player Characters as Vampires sidebar, Monster Manual page 295, and go from there. Other than their special abilities, which they probably wouldn't be able to use once they became Ghouls, Dryads are fairly similar to humanoids, so the Ghoul statblock shouldn't need much alteration to represent Dryad Ghouls.
Best Answer
No canonical list
There is a very obscure list, but it was printed long after the concept of forks for plane shift first originated, so for a long time there was no list. And that list was published in Dragon magazine and never again referenced, making it largely unknown; the overwhelming majority of tables will be unaware of it. In such a case, you’d have to ask your DM if it is relevant to you. On some level, there is supposed to be a specific metal for each, but what exactly is the DM’s call unless he uses that obscure Dragon article.
For reference, I’ve checked the Manual of the Planes, the Planar Handbook, and searched online for any kind of list, official or otherwise. I could not find any, nor have I ever heard of one. I’ve also checked with a friend who knows a lot about Planescape, and he stated quite definitively that no such list exists.
A comment about rationale
The rules regarding the foci get... a little wonky, to be honest. I’ll get into details below. But I think a reasonable interpretation can be found which fits in neatly with the fact that no such list exists.
It seems to me that the forks for the major planes are “negligible,” that is, found in any spell component pouch (or obviated by the Eschew Materials feat), but it is possible for obscurer planes to require forks not typically found in the pouch. So basically, there is no point to any list, because if the plane is a big enough deal to show up in the books, it’s a big enough deal to just be in the pouch so you don’t need to worry about it. If it actually needs something special, by definition it’s something small and unique to a particular campaign, so the book can’t describe it.
What the rules actually say
As I said, the rules get wonky. Here is what we have:
Rules as written
RAW, the foci for plane shift do not have a listed cost: thus they are considered negligible and covered by a spell component pouch or the Eschew Materials feat.
Note that this is despite the fact that the class spell lists have F (my thanks to @insomniac for pointing this out), as in
and the rules for spell lists state that
The class spell lists are secondary sources for spells; they are supposed to indicate, in brief, information already included in the full spell description. Since the primary source for plane shift, that is, the full spell description, does not indicate that the focus component is non-negligible, it isn’t.
Intent?
What was intended is debatable; either they intended the forks to be non-negligible, and forgot to indicate this in plane shift’s full description, or they intended the forks to be negligible, and forgot that the F is only for non-negligible foci (or they changed their mind at some point and forgot to update one or the other).
My interpretation, based on the rules
Or, and I actually think this is the most likely case, plane shift’s focus is sometimes negligible, sometimes not, and the spell list short description is too brief to get into that, so the F is used to indicate that the spell can require a non-negligible focus. Note that miracle, for example, appears in the cleric spell list as
even though only some uses (“powerful requests”) of miracle cost XP, while others (the spell-mimicking options) do not.
I think this is what was meant because plane shift itself has a caveat that certain planes may not have easily-available foci. So I think that, generally speaking, a well-stocked spell component pouch should include all major planes, but, for instance, the personal demiplane of a recluse wizard, probably not so much. A DM may choose to make this more or less of an issue, but this is always a matter of plot and not of balance.