Hmm, I was thinking of a command for it to go find food, and I was originally thinking a dragon, that you had to do a quest to get, and would follow you around and you'd have to feed him everyday. Eventually he'd get bigger and bigger until he's a little bit bigger than the character and than he'd be an advlt. Halfway between his advlt transformation, he would start flying. Instead of following you everywhere you go, he'd fly, you'd also acquire spells based on him, such as a disarm, where he would fly down and take their weapon. I don't know, just my idea.
As for the other ideas, I will definitely use a lot of them. Keep this thread going though, I'm interested to build the best animal companion.
You might want to get http://www.tesnexus.com/downloads/file.php?id=9562 and crack it open in the CS. It includes a tiger companion that you can feed and it gets bigger as time (or feeding?) progresses.
Also, you could look at http://www.tesnexus.com/downloads/file.php?id=26723. IMO one of the coolest mods ever made. It includes a constant animal companion (bear, wolf, or lion) that comes with many commands like attack, run away, defend me, wait, follow, etc.
The best animal companion I could have for my archer character would be a hawk, following me and spotting enemies from a distance.
That is an AWESOME idea. And totally simple I think. You could get a hawk (or other flying creature) from http://waalx.com/RealSwordsForum/index.php. Waalx will typically allow people to borrow his animal creations to make mounts and companions, as long as you're not simply re-releasing them with no modifications. But it's always good to ask. I got a crow for my Druid Mod Remade.
As far as how it would work, you could have a quest script going whenever you have summoned or activated your hawk. The quest script could have a one-second interval between executions. In that script, you could simply check to see if any creatures or NPCs are within a set distance from you, then check to see if they are hostile. And if so, the script could play a hawk screech sound.
I did almost exactly that in my http://www.tesnexus.com/downloads/file.php?id=37894. While shapeshifted into wolf form, you can activate a "danger sense." If any hostile creatures or NPCs are within 80 feet, you growl and glow red for a second. Because you smell danger