Fuzz and Distortion EffectsA fuzz, overdrive or distortion is perhaps the first thing that comes to mind when people think about guitar effects and for many it is their first pedal. I dare say that for most it really is their first effect as most amplifiers do some form of this.
Sites with multiple fuzz and distortion circuitsBeavis Audio Research - Four Knob Rat, Fuzz Lab Jr, ScreamerLab, Trotsky Drive, Valve Caster.
Tonepad - Ampeg Scrambler, AMZ Overdrive Pro, Big Muff Pi, Blue Clipper, Blues Breaker, Boss DS-1, DOD 250 Distortion, Easy Face, Fuzz Face, Guvnor, MXR Distortion Plus, Rat, Sans Amp GT-2, Tone Bender MKII, Tonebender 3 Knob, Tube Screamer, Tube Sound Fuzz.
Run Off Grove - Double D, Eighteen, The English Channel, Flipster, Grace/Big Daddy, Matchbox, Mockman, Peppermill, Professor Tweed, Supreaux Deux, Thor, 22/7, Tube Reamer, Umble, Uno.
Non tubeBig Bastard - Also known as Big B*****d, high gain.
Big Daddys Bastard Sister - Related to Big Bastard.
Big Muff - Classic(ish) fuzz in multiple variants.
Fuzz Face - Legendary fuzz circuit.
Fuzzrite - Another legendary fuzz circuit.
Proco Rat Distortion - Veroboard layout.
Professor Tweed - JFET tube emulation goodie from ROG.
Pushme Pullyou - Octave fuzz.
Rump Roast - Can also be wired as a booster.
Suzy Q Harmonic Clipper - Adaption of a Kustom amp channel by (Pink) Jimi Photon.
TubeMatsumins Valve Caster - Tube boost and light overdrive.
Spark Gap - Tube Screamer with tubes!
Tube Star - More gain that Matsumin
Shaka SubCaster - Shaka Tube with submini tube, thread also has information about Shaka Tube.