Chuck Liddell was tough in the last era of the UFC, before fighters had to have a "complete package" of skills. He fought some good fights and I enjoyed watching him for a good 7-8 years (as long as I've been a fan of MMA). Towards the end his chin really became a major problem though. I don't think he can take a big punch anymore without getting KO'd.
The only fighter I can think of to list as truly "overrated" is Tito Ortiz, as he hasn't proven anything in a long time. He's still part of that last-era and though he's tried to evolve, isn't up in the same caliber as the new breed of UFC fighters. I can understand his marketability, in the past, but even that's on it's last leg. I see him overseas or in the independent circuit doing announcing, or something. I think Dana really hates this guy, and so do I.