Goblin Rabblemaster seems to be pretty high on the raw power scale, but he's gotta fight int he paint and is super removable. He's probably nuts in cubes where games are generally low interation races, or at least as nuts as a 3 drop gets.
Cruel Sadist and Wall of Limbs are not going to be run as written.
Inferno Fist sucks, but my friend thinks it'll be really good in my list, so I put it up here.
I was going to try Genesis Hydra, but the fact that he is "scalable" doesn't seem to play considering how often he'll be just awful at X < 4
Jace isn't nearly as bad as people are saying he will be and one day he might get played. Probably after the price drops. Spectra Ward is pretty annoying, but it actually doesn't seem like its really that great unless it goes on a doublestriker. 5 is a lot.
Soul of Innistrad and Soul of Theros both seem pretty legit, but those slots have a lot of other options that might be more interesting.