Is there much concern with how balanced the end results are? Or, so long as it's fun to play and not mind numbingly broken, you don't care? Just curious... Till I know, i'm going to work on the assumption that the Beast Tamer, which is likely a mostly noncasting class, should be equal to the Summoner being made in power. Sicne casters are quite strong in 3E, the Beast Tamer will NOT look balanced compared to say...Fighter.
For a Beast Tamer...I think the easiest starting point is to use the Ranger class's framework -- d8 HD, Fort and Ref as the good saves (same as animals get), full BAB, and a good amount of skill points. 4 + Int or 6 + Int, depending. Roughly the same class skill list, too.
A Beast Tamer should definitely have Wild Empathy, and probably get a bonus on it of some sort (+1/2 class level?). A few levels in, you can remove the -4 penalty for using Empathy on magical beasts. Animal Companion is another obvious thing to steal. Give them full Druid levels, not the Ranger's crappy 1/2 levels. At higher levels, allow more companions, and also expand the list to include low int magical beasts.
I think Beast Tamer's primary stats should be Str, Con, Cha, and (maybe) Dex. Most class features that involve an ability score should involve charisma.
Instead of spells per day, I like the idea of spell-like abilities since they're more "primal." Instead of fixed spells gained, give the BT a small spell list that he can choose to spontaneously cast his spell-like abilities from, sort of like how Factotum works... The spells would mostly be from the Druid and Ranger lists...I don't feel like searching for the best candidates right now.
You can also give the BT Bard/Marshal-like group buffing abilities, that only function on animals and magical beasts. Not just simple +x to hit stuff, though. Let him give creatures temporary usage of special attacks from the monster manual they may nto currently have. Like ordering a grizzly bear to pounce. Or giving a Hydra a rend attack. I don't know, might get broken, but it could be cool.
Other ideas:
Class feature that forces any low int creature trying to attack the Beast Master to make a will save or else heel and cease being aggressive towards him unless he does something to provoke the beast. Saving should make the beast immune to the effect for 24 hours.
Ability to train an animal and teach it tricks in a mere fraction of the normal time required.
Ability to teach animals more tricks than they could normally learn, and also teach "advanced tricks" beyond the scope of what an animal could normally be trained to do.
Expand the animal companion benefits to all allied beasts. At the very least, give Devotion to all of them...otherwise this class is a walking target for any enemy with will save spells...
