Cheapy CA-30 (Korg IIRC) works fine for me. I've not managed to break it yet, which indicates some resilience. And it's cheap, and it's chromatic, and it just works. I've seen lots of cool flashy ones (Intellitouch have a *very* high Gadget Factor Rating) but never felt the need. Having said that, I like Clinton's idea of an in-line tuner pedal so you don't have to disconnect.