Box of Rock - Available in Hand Painted USA made, or Vexter version.
This pedal has two effects in one box, a clean boost and a distortion circuit.
The Box of Rock (TM) is Z.Vex Effect's first "distortion" pedal, highly specialized to simulate the "everything on 10" sound of a classic Marshall JTM45 non-master-volume amplifier. You may use the Box of Rock effectively with many different amplifiers, but to get the sound I heard when I designed it, try it through a Marshall at least once. You may use your guitar's volume control to adjust for the exact amount of distortion you need, all the way down to very clean and clear with most drive settings. You will notice the words "distortron engine" on the Vexter version of this pedal (no, that's not a misprint) on the pedal. This is what I named my distortion circuit... call me crazy. On the hand-painted version, the stomp switch on the right is labeled "ROCK" instead, because our paint brushes are too wide for so many small letters.
The Box of Rock also contains an extremely high-headroom, unity-to-50X gain booster with nominal input impedance and low hiss. It is very similar to the SHO boost circuit, with refinements to make it sound more like a standard amp input and less glassy. The boost channel can be used alone or in conjunction with the "distortron engine" channel. The boost channel follows the distortion channel so that the distortion is able to hit your amp harder (at a higher volume) when both switches are engaged, for boosting solos and what-not.
For more info and video and audio samples: http://zvex.com/boxofrock.html
For a .pdf version of the Box of Rock instruction sheet: http://zvex.com/Box_of_Rock.pdf