I've seen one or two Pantheons do rather well in mid, using Pantheon's great early game to shut down the opposing AP mid. I'm unsure however as to who he was facing up against.
I'm really interested in Urgot, as he's someone people rarely use, and although I know people know of him and have used him mid, has a ton of potential. Between that zoning potential, and that ult, h'o man. (Urgot's free this week, I challenge everyone to roll up in blind pick and try some of this out... no bonus points if you infuriate people in ranked)
Then there are champs that I'd think would be really dumb to try out, but could possible be a counter to one or two specific AP mids. People like twitch or Mundo (I mean, he does go where he pleases... mid lane is no exception), could be interesting if you found that they countered a certain aspect of a traditional AP mid.