Choose from pedal tuners for stage use, Chromatic versions that will let you use altered tunings on your guitar, DADGAD or Drop C for instance, and the modern clip-on style of guitar tuner.
Clip-on versions work by vibration rather than by picking up sound waves. This means that they can be 'clipped on' to the head stock and it picks up the vibrations through the instruments wood. As it resonates, it sends vibrations around and up the neck to the headstock where it will be mounted. These are good for useing when there is background noise as they aren't affected by sound waves. These are ideal in a gigging situations.