If there were other people with superpowers, the only thing I'd need is a Peter Petrelli-ish power to imitate them, even remotely.
However, if it was just me, I'd like to:
1: Manipulate probability
2: Make duplicates of myself
3: Be able to accurately mimic physical skills, like knitting, guitar playing or awesome kung fu
That way I could kick so much ass. I could beat a villain, using what I effectively learned watching kung fu movies, while he randomly tried to find the "real" me, but I'd make that statistically unlikely. Also, when I'm finished mopping the floor with the bad guys, I'd replicate myself into a full hard rock band, then have some sweet sweet lovin' with all the hot groupies at the same time.
And if I ever felt cold, a duplicate of mine could knit me a nice sweater.