Here's a cool overdrive circuit designed by Martin from SoulSonic FX. It's said to be a "Klon Killer," so if you've been disappointed by that circuit, give this one a go. Signal goes through a buffer then is split between clean out put and the rest of the effect. So not a true-bypass effect, but having a buffer in your signal chain won't kill you. And the buffer on this thing is really top notch. For switching use one side of a DPDT for the effect, and the other for the LED indicator. For more info and the schematic, check out the thread on FSB.