Guitar tuners are a dime a dozen, including ones with little motors that physically turn the pegs to Gibson's fully automatic "Robot guitars." Separate tuners are difficult to find when you're on stage, however, and the Robot guitar, while interesting, makes you play on an entirely new guitar. (And pay over two large for the privilege.)
I think the new "N-Tune" tuner is a nice compromise. It's basically just a simple digital tuner as found for $15 on the shelves of any guitar shop, but designed to slip under your existing guitar's volume knob. Pull the knob out and the N-Tune activates, cutting off output so you don't sound like a twerp while tuning back in. The tone to which the N-Tune thinks you're trying to tune lights up, while a green LED activates when you're on pitch.
The N-Tune is going to be $100 when it's out this month. Some installation will be required, of course, but nothing too onerous. They're sending me one to test, so I'll be digging into my Mexican Telecaster to do my own install. My thrash metal cover of "Froggy Went a'Courtin'" will sound better than ever.
Product Page [N-Tune]