Boss TU-3 US Chromatic Tuner, Convenient Pedal-Based w/21-segment LED meter
You need this pedal. Period. Whether you play acoustic guitar, electric guitar, or bass, you need to be in tune. No amount of friends in the crowd will save you from bombing if you're up there making a fool out of yourself because you're obviously out of tune and unprofessional. Think of Boss's TU-3 tuner pedal as your best friend onstage. It's stupid-easy to use, it's easy to see even in bright sunlight, and it's built to keep you sounding good for years to come. You get all kinds of modes that let you tailor the TU-3 for your particular setup.