NPD: Boss EV-30. This is so much fun with the Keeley Monterey. It's a dual expression pedal so you can control two different pedal exp. outs from one treadle. I'm thinking of
Guitar Pedal X - GPX Blog - 9 of the Best Guitar Expression and Volume Pedals for Your Consideration
Quick Hit: Boss EV-30 Dual Expression Pedal Review - Premier Guitar