The market for clip-on tuners has grown rather crowded ever since Intellitouch made a big splash back in 2001 (we do, of course, still sell Intellitouch). With new brands upping the ante in both performance and affordability, it seems like there's always a new, better clip-on to beat last year's model. The good news for guitar players like you and me is that this means these things just keep getting better.
The undisputed king of the hill these days has to be Snark—it outsells all other guitar tuners by a fair margin. It's not hard to see why: Every Snark grabs notes quickly and accurately, the display is uniquely easy to use, and the price is very appealing. Moreover, the SN-8 listed here features a tap tempo metronome (unique among clip-ons), an internal mic (also unique), wide pitch calibration, and a transposition feature. If you're in the market for a clip-on, you'd have a hard time doing better than this. Plus, if you're looking for a pocket tuner, Snark's other tuners (they call them "console tuners") are also worth a serious look.