Boss MT-2 Metal Zone
The Metal Zone gets a lot of hate for having a thin and shrill sound, but there's a lot more going on here. Name another pedal with four tone controls! If you need to make a Telecaster and a keyboard amp sound like metal, this will do it. And even if you have all your distortion needs managed, this pedal can still be used as an instant feedback circuit. This one is pretty old, and has seen much better days.