Here is my list:
1. Nate Robinson.
I soooo rooted for this guy. At his best he was such an exciting player, sort of a supercharged Vinny Johnson. He was (and is) a flat out amazing athlete.
2. Von Wafer.
Believe it or not I had really high hopes for this dude. In 2010 he started taking the ball to the basket, making his 3s, and really contributed as the year went on. Usually guys that get better throughout the course of the year just keep getting better in the offseason. Didn't happen with Wafer and it really disappointed me.
3. JJJ.
This one really hurt. He seemed like a guy with multiple offensive moves and a nice little midrange jumpshot. At one point he seemed to be coming on defensively, but his progress stopped, he was shipped out of town, and we never heard from him again.
4. Semih Erden.
Could block shots, could finish with both hands, could rebound, could play. What happened to you, Semih?
5. (the big one) Mike Bibby.
Ok, he wasn't exactly a bust, but when I first started watching him as a young player with those exciting Sacramento teams, I thought he was the next Isaiah Thomas. In his early days his jumpshot was dynamite. Could get it off against anybody. Fearless, too. A young kid not afraid of the big moment whatsoever. He stopped getting better and never turned into the player he could have been.
6. Leon Powe.
A 6'5 power forward and a great story. Was in the top 10 in NBA efficiency one year. Could run. Could jump. Great moves around the basket. Got hurt and disappeared.
7. Glen Davis.
"He tiptoed through the tulips on that one, huh Tommy?" (Mike Gorman)
Another guy not afraid of the big moment. Very crafty with his body. Very good in pressure situations. Fell in love with his crappy jumper and is now looking for a job as I understand it.