I’ve tried several clip-on guitar and banjo tuners over the years, and I finally found the best one: Snark SN-2. It’s fast, easy to use, and very accurate. Best of all, it’s cheap: $13. It’s optimized for all instruments. If you only need it for guitar, get the $10 Snark SN-1.
The build quality seems better than the previously reviewed Intellitouch, and the display is much nicer (glasses not required). And it’s really fast and responsive. Plus, it has a “tap tempo” thing so you can tap the button along with the tune and it will tell you the beats per minute.
I’ve been reading about it on various forums, and I haven’t found any negative comments — except for the colors. For a little bit extra you can get a black model.