4. ProCo Rat
Despite being first produced in the late 70s, this pedal really started to dominate the musical landscape in the 1990s, with James Hetfield, Thom Yorke, Kurt Cobain and James Dean Bradfield all using the Rat to great effect.
The op-amp circuit is simple yet beautiful, and provides a dirty and powerful distortion which can be heard on thousands of hit records.
You voted it as the fourth greatest distortion pedals of all time.