Having a quality tuner is essential to your practice. You should tune your guitar each time before playing. Hearing your guitar in tune actually helps train your ear to learn correct pitch.
The Sabine STX1100 Chromatic Tuner is not the cheapest tuner on the market, but for a few dollars more, it is absolutely one of the best! It features in and outputs for electric guitar, and a built in mic for acoustic.
If you are looking for a live in line tuner, the Boss TU-2 Chromatic Tuner is an industry standard. I have seen these tuners literally stomped, crushed, dropped, and lit on fire; and they still work. They could almost be called indestructible!
