I'm using the small fluval prefilter. It's small, effective, and looks sharp. The big drawback is it clogs quickly... I'm lucky if it lasts a week.
I had this guy a while back, and it was amazing. http://www.amazon.com/gp/aw/d/B0002565HU/ref=mp_s_a_1_1?qid=1378152332&sr=8-1&pi=AC_SX110_SY165