1. Lil' Marrowgar. ICC may be a thing of the past, but that doesn't stop me from wanting a Lil' Marrowgar bonestorming his way through the enemy pet team.. just imagining "Bonestorrrrrrmmmmmm" in a high-pitched Lil' KT-style voice makes me crack up.
2. Stunted Yak. Yaks are one of the coolest creatures on Pandaria, how on earth we didn't get a battle pet of them at Mists launch is beyond me. /glare
3. Grummle Trail Guide. Lots of people love grummles and there don't seem to be a great deal of humanoid pets in the game - two birds with one stone!
4. Lil' Festergut/Rotface. Call me nuts but I've always have a soft spot for these 2, they were essentially 2 big (evil, undead) kids trying to please their dad. Battle pets of them could be a lot of fun, I think.
There are tons more I can think of, but I'll stop here. For now!