I'm using a Corsair H50 as the cooler. It had lots of good reviews and takes up much less space than the huge air coolers.
Precisely why I got mine. I can't fit any big tower coolers in my case, else I would have gotten a Tuniq Tower 120 Extreme (damn that thing's pretty!). It also lowered temps by 10C load from the Core Contact Freezer I had before it, and I even clocked it 200MHz higher.