If we're talking about recent WR busts, then Jordan Murphy has to be in the conversation. Blue chip recruit, also recruited by Bama and Ole Miss. Had a terrible attitude, lousy work ethic, and basically did very little while he was here. Eventually left the team after the Georgia State loss. Not picked up by anyone else since then.
As for Banks, what happened with him? He had a great Sophomore season. I know he got dismissed from the team, but was it just for smoking pot? I don't know that you could call him a "disappointment" at WR; he was actually quite good at it. Just got booted from the team.