Animal husbandry looks cool, but I’m not sure exactly what counts as a trick?
Could something like a snake be taught tricks too?
Ever watched performing animals (whether on the street or in a circus or show), seen animals doing tricks on t.v., watched animals trained for specific tasks in action, or watched a film featuring live animals that were trained to do certain tasks? All examples of tricks. Roll over, play dead, attack, beg, fetch that, bark, limp, track, ad nauseum. The more intelligent the animal, the more involved the tricks and actions it can be trained to do. That leads us nicely to snakes; some animals (such as many reptiles) simply don’t respond as well to training, so you’re going to have to judge that yourself based on your own experience of animals (even as a spectator or watcher) and a bit of research online. There are too many cases for a rulebook to cover them, so get out there and do a little searching. 
In this case you might want to take a look at the 3.5 SRD - it lists several standard ‘tricks’. Then you can get creative and branch out from there.
Ignore the DC stuff, from the SRD:
“Push” an Animal
To push an animal means to get it to perform a task or trick that it doesn’t know but is physically capable of performing. This category also covers making an animal perform a forced march or forcing it to hustle for more than 1 hour between sleep cycles. If the animal is wounded or has taken any nonlethal damage or ability score damage, the DC increases by 2. If your check succeeds, the animal performs the task or trick on its next action.
Teach an Animal a Trick
You can teach an animal a specific trick with one week of work and a successful Handle Animal check against the indicated DC. An animal with an Intelligence score of 1 can learn a maximum of three tricks, while an animal with an Intelligence score of 2 can learn a maximum of six tricks. Possible tricks (and their associated DCs) include, but are not necessarily limited to, the following.
Attack (DC 20): The animal attacks apparent enemies. You may point to a particular creature that you wish the animal to attack, and it will comply if able. Normally, an animal will attack only humanoids, monstrous humanoids, giants, or other animals. Teaching an animal to attack all creatures (including such unnatural creatures as undead and aberrations) counts as two tricks.
Come (DC 15): The animal comes to you, even if it normally would not do so.
Defend (DC 20): The animal defends you (or is ready to defend you if no threat is present), even without any command being given. Alternatively, you can command the animal to defend a specific other character.
Down (DC 15): The animal breaks off from combat or otherwise backs down. An animal that doesn’t know this trick continues to fight until it must flee (due to injury, a fear effect, or the like) or its opponent is defeated.
Fetch (DC 15): The animal goes and gets something. If you do not point out a specific item, the animal fetches some random object.
Guard (DC 20): The animal stays in place and prevents others from approaching.
Heel (DC 15): The animal follows you closely, even to places where it normally wouldn’t go.
Perform (DC 15): The animal performs a variety of simple tricks, such as sitting up, rolling over, roaring or barking, and so on.
Seek (DC 15): The animal moves into an area and looks around for anything that is obviously alive or animate.
Stay (DC 15): The animal stays in place, waiting for you to return. It does not challenge other creatures that come by, though it still defends itself if it needs to.
Track (DC 20): The animal tracks the scent presented to it. (This requires the animal to have the scent ability)
Work (DC 15): The animal pulls or pushes a medium or heavy load.
Train an Animal for a Purpose
Rather than teaching an animal individual tricks, you can simply train it for a general purpose. Essentially, an animal’s purpose represents a preselected set of known tricks that fit into a common scheme, such as guarding or heavy labor. The animal must meet all the normal prerequisites for all tricks included in the training package. If the package includes more than three tricks, the animal must have an Intelligence score of 2.
An animal can be trained for only one general purpose, though if the creature is capable of learning additional tricks (above and beyond those included in its general purpose), it may do so. Training an animal for a purpose requires fewer checks than teaching individual tricks does, but no less time.
Combat Riding (DC 20): An animal trained to bear a rider into combat knows the tricks attack, come, defend, down, guard, and heel. Training an animal for combat riding takes six weeks. You may also “upgrade” an animal trained for riding to one trained for combat riding by spending three weeks and making a successful DC 20 Handle Animal check. The new general purpose and tricks completely replace the animal’s previous purpose and any tricks it once knew. Warhorses and riding dogs are already trained to bear riders into combat, and they don’t require any additional training for this purpose.
Fighting (DC 20): An animal trained to engage in combat knows the tricks attack, down, and stay. Training an animal for fighting takes three weeks.
Guarding (DC 20): An animal trained to guard knows the tricks attack, defend, down, and guard. Training an animal for guarding takes four weeks.
Heavy Labor (DC 15): An animal trained for heavy labor knows the tricks come and work. Training an animal for heavy labor takes two weeks.
Hunting (DC 20): An animal trained for hunting knows the tricks attack, down, fetch, heel, seek, and track. Training an animal for hunting takes six weeks.
Performance (DC 15): An animal trained for performance knows the tricks come, fetch, heel, perform, and stay. Training an animal for performance takes five weeks.
Riding (DC 15): An animal trained to bear a rider knows the tricks come, heel, and stay. Training an animal for riding takes three weeks."
With a snake, I would imagine snake charming being a typical trick.
So general attack/defend commands
but how about something like teaching a wolf to trip people? That’s a special attack.
Could I teach an ape to hurl big rocks or use a sword?
Dude, what makes you think people are going to have definitive answers for such questions given that no one has ever taught a wolf to just trip people or an ape to attack with a sword? Go and do some research into what apes and wolves (and related species) have been taught to do, and make some decisions. I mean, seriously, if canines could be taught to effectively just “trip” folks, don’t you think they’d have taught guard and attack dogs to do that (instead of which they’re trained to attack the arm and drag down on it to immobilize)? Also, given that chimpanzees have been filmed clubbing animals with heavy sticks in the wild, it wouldn’t be much of a stretch to imagine them being encouraged to do so in captivity. Wielding a sword, on the other hand, is a whole different ballgame. I’m not saying this to be awkward, but you really need to do some digging yourself. I wouldn’t have half the general knowledge I have (especially about natural history and military history) if I hadn’t done such digging myself.
I remember playing Dragon Age and having a bloody great Dog knock me to the ground and start eating my face. Could be represented by trip… Likewise grabbing someone’s hand to immobilise them could be represented by the Wrestling manoeuvre.
Snake-wise, I’m sure I’ve seen people in fiction with tame snakes kept about their person who rear up to defend them when threatened… Or calm down when told to by their owner, as the mood is sufficiently cowed by the snake. 
Imagination and DM buy-in are key, but there’s a whole bunch of examples in fiction to draw on.
A guard-ape with a sword and shield is a hysterical idea, and I’m kind of in favor of it. That doesn’t mean I’ll allow it, of course.
Present-day scientists have hardly been able to come to a consensus on how intelligent and trainable animals are. I think this is partly bias, and partly because animal IQ might vary from animal to animal quite wildly. So you have wide latitude here as Judge.