Sean O'Haire vignettes were some of the best EVER, they completely dropped the ball with him.
Also I'd add The Brian Kendrick word, is he did it to himself, but which every way you slice it, he had what seemed like a great character and ultimately went nowhere with it.
And while I'm at it, Billy Kidman, admittedly he was partially damaged goods when they got him, but they could have done more with him, his team and subsequent feud with Paul London was great while it lasted but it just seemed to vanish/filter out in no time.