Digitech makes an OD pedal called a Bad Monkey, and a gent named Scott Humphreys mods them for guitar or for bass. The result is the Baddest Bad Monkey. I have the Humphreys bass mod version. To my ear it's the most realistic OD pedal, and it has a decent range of adjustment.
Here's a great story - I bought this pedal used on Ebay, and emailed him to ask which version I had. I intended to pay for him to tweak it if the version I bought was the guitar one. He told me to send it in and he converted it at NO charge - all I paid was shipping. He is a real gentlemen in my book!
