Dragon Age 2. I almost always wait to buy games until they get under the $20-$30 mark, but was pretty excited about DA2... definitely regret purchasing that at full price. Going through the same areas over and over killed it for me. Still beat it, but really wish I hadn't paid full price.
Other than that, there is probably a bunch of steam games I really didn't need to buy, but they were so cheap so I don't care that much.
I was thinking about starting Far Cry 2 soon, but looking at the consensus here I might just hold off on that one. Got it for free on PS+ anyway.