There are hundreds of different stomp boxes out there for guitar, but without a doubt one of the most useful is the humble guitar compressor (also called a sustainer by some guitar pedal manfacturers).

 

A compressor-sustainer can add a smooth singing sustain to leads and a punchy attack to chords, resulting in a powerful guitar sound that sounds more professional and polished. eBay auctions have hundreds of vintage and classic guitar compressor pedals available. Bid on a classic  today and save big!