Bubs, Venerable Strongheart Halfling Commoner3/Marshal1
Traits and Flaws
Flaw - Flexible Mind = +1
Human - Animal Affinity
1 - Skill Focus: Handle Animal
3 - Dinosaur Wrangler
Cha can be as high as 22 (18 base, +3 age, +1 ap)
Buy an Animal Trainer's Kit
Beg the DM for a custom item of Handle Animal (we can technically afford up to a +7 item, depending on your cheese tolerance).
Activate a Marshal Aura of Motivate Charisma.
Become an affiliate of the "Animal Domain" organization (Complete Champion page 30); you only need a +4 affiliate score, and taking full ranks in Handle Animal and Know:Nature gets you there.
Total Handle Animal score: 37 (7ranks +6cha, +6aura, +7 item, +2kit, +2affinity, +3focus, +2affiliate, +1trait, +1flexible), with an additional +4 against Dinosaurs.
Now, the DC to rear a wild animal is 15 + the animal's HD, and doing so gets you up to three of that kind of animal. The DCs to train it afterwards are constant, so that's good. Assuming take 10 is allowed, or we get merely average rolls, we can reliably rear wild animals of up to 32 HD. This includes such fun ones as the Dire Rhinoceros (CR 9) and Dire Elephant (CR 10). However, we also get a +4 with Dinosaurs, raising the limit up to 36.
If you guessed that I was going to roll out a 36 HD dinosaur, you're on the money. Meet the Battletitan. At the low end of CR 16, it's not going to be soloing the Tarrasque any time soon. But with AC 35, four natural attacks that are not going to miss, legendary hp, impressive saves, a Str score better than a Storm Giant, Improved Grab, and a buttload of feats to customize with... yeah, you'll be travelling in style. And for all your effort, you get three of these.
At level four.
(edit - You can also raise Magical Beasts of up to 17 HD. I'm sure there's all sorts of fun there, too, but I'll leave that as an exercise to the reader.)
(edit2 - Couldn't resist. Here's a partial list of possibilities: Chronotyryn (CR 19), Disenchanter (CR 17), 12-Headed Cryohydra (CR 13), Nightmare Beast (CR 15), Spellgaunt (CR 12). Unfortunately, training magical beasts is considerably harder, as apparently they're willful folk. Might not take kindly to some ancient, shrivelled halfling giving them orders. Still, hey, roll a 20 and you've got it. And if you've got a trio of pets with Time Stop as an SLA and Dual Actions, you shouldn't have much to worry about.)
(edit3 - Battletitan flavour, just for the win: "Battletitan dinosaurs are massive predatory beasts meticulously bred as hybrids of other dinosaurs. They do not occur naturally; only elaborate nonmagical breeding techniques give rise to the mighty battletitans. Kingdoms that fi eld the dinosaurs in their armies jealously guard the means of their creation, treating such information as a state secret. With the ferocity of the most dangerous carnivores and the defenses of the toughest armored herbivores, a battletitan is a terror to behold." Three of them.
You just know I'm going to be heartbroken if someone finds a hole in my build...)