I use the Moog EP-3. It's $40. Works great and you can set the range on it like a wah pedal.
Only thing I don't like is when you use an expression pedal on the REV2 for volume, it also silences effects like reverb and delay. On my OB-6 when I use the same pedal, effects like reverb and delay still ring out after you bring the volume down which makes for great "swells" or quick stops where the effect tails still happen.