2004 NFL Draft: Chris Perry, RB (Michigan)
After some trades (and one that led to Cincinnati missing out on Steven Jackson), the Bengals ended up with the 26th overall pick in the 2004 NFL Draft and used it on Michigan running back, Chris Perry. The pick wasn't great, as Perry finished his NFL career (all spent with the Bengals) with just 1,080 scrimmage yards and four total touchdowns.
Injuries killed Perry's career, as he was injured during his rookie season and that led to him carrying the ball just twice. He missed most of the 2006 season and all of 2007, both due to injuries, and while he finally got a chance to show what he could do in 2008, he failed to prove himself.
I hate labeling injury-prone players as busts but Perry falls into the bust category. He had just 606 yards on the ground and two rushing touchdowns in four seasons.
2005 NFL Draft: David Pollack, LB (Georgia)
After a stellar career at Georgia, the Bengals made David Pollack the 17th overall pick of the draft and decided to move him from defensive end to linebacker in their defense. Things got off to a decent start, as Pollack showed the potential of what made him a first-round pick in 14 games with 28 tackles and 4.5 sacks.
Unfortunately, Pollack's NFL career was a short one, as he was injured in Week 2 of the 2006 season (just his second year in the league). He collided with Browns running back Reuben Droughns and suffered a neck injury. He missed the rest of the 2006 season and the entire 2007 season and then called it a career in 2008.
As is the case with Chris Perry, it sucks that players whose careers were shortened by injuries are often listed as draft busts but that's how it goes.