MXR M108S (new silver one with really bright fucking LEDs!!)
I have a couple - I think they're up there with "indispensable" and "mandatory" pedals. No other pedal has done more for me in getting that extra 5% of perfection outta my amps/cabs.
Sometimes even use one in-front, and one in the loop... Love 'em. Cheap, quiet, effective, and comes with PS. No complaints. Perfect for my needs. And no, I don't obsess over the Constant-Q or "highest quality evar" stuff in this case. It's got sliders, it does what it's supposed to, and sounds dope, at a kickass price.