Jarrod Maidens. Was supposed to be a mid first rounder in his draft year, hasn't played in a season and a half, and could really be a steal if he becomes healthy again.
I'll second that. Former #4 overall OHL pick, was off to a great start in his draft year, and then gets concussed and hasn't played a game since. He could come back and blow people away, or fall on his face. Very interesting situation.
As Datsyuk said, it's hard to be too in depth with anyone but your own guys, so for the Leafs, I'll go with our 7th rounder this year, Andreas Johnson. Led Frölunda J20 in scoring with 54 points in 42 games, and was more than a PPG at the U19s, too. He's a shrimp at 5'10, 170lbs, but the Swedish posters tell us he's fast as hell and he's got some pretty nifty hands, too. As a 7th rounder, I highly, highly doubt he turns into anything, but he's a skilled guy, and I'm actually excited to see what he can do next year in the SHL
Beyond that, Reid Boucher gets surprisingly little chatter despite breaking Stamkos's club goal scoring record. I'll be keeping an eye on him.