Silent Hill Downpour. I have it on 360 and it freezes for a second or two every 3 seconds. That isn't an exaggeration by the way. It's literally: Take 3 steps. FREEZE. Take 5 steps. FREEZE. It only happened when I did every sidequest, but that's hardly acceptable.
Borderlands. It doesn't have any frame-rate issues by default, but it often drops to near unplayable levels when a lot of things happen at the same time. Luckily, those frame-rate drops only lasts for very short periods of time before going back up again.