one like this: http://www.musiciansfriend.com/srs7/g=guitar/s=accessories/search/detail/base_pid/361600/

or one that looks identical to that one. it's best because you can take it off, put it on, or move it in like 2 seconds with one hand, I've seen other capos where you've actually had to put it on, and the turn two litte screw type things to make it tight... took like 2 minutes to put on... not good if you need to do it fast in between songs or something... plus one like the one I posted can be clipped onto your headstock when not in use so it's always in reach when you need it.