Honestly........I would say FreeCreditReport (is that even up anymore?) or maybe Netflix, even if it doesn't credit instantly. I mean, what a great excuse to sing up for Netflix? lol As for Free credit report, it credits fast and has fairly good money rewards, and as long as you read the fine print, you're fine. There's probably a lot more, but I don't do a lot of the CC ones.
Oh here's another tip--be careful with Emusic if you sign up for a plan. They''re kind of expensive if you click the wrong thing....