Blood Hawk

Basically an eagle with slightly bigger numbers. One magical beast HD, small size, 80 ft. fly speed, three natural attacks (that all inflict bleeding wounds), and reasonably good stats (13 strength, 16 dexterity, 11 constitution). Additionally, a blood hawk who 'advances to become a creature with more than 1 HD' gains Ferocity, allowing it to keep fighting even when dying.

Low intelligence is a pity, as is the lack of hands, but with no real HD penalty I'm willing to say this would be able to keep up with an at-level party. Go rogue or something (preferably after finding a way to get more intelligence), or just be a wisdom caster and zap stuff from above.

+0 LA for now, entertaining thoughts of -0.