Over the years several companies have tried (and failed pretty miserably) to create a natural-sounding feedback generator, but we were pretty impressed with the new FreqOut pedal that DigiTech brought to NAMM. You can select whether the footswitch simply engages the effect or is a momentary switch, but either way you get convincing feedback and sustain in seven settings (including 1st, 2nd, 3rd, and 5th harmonics). A dry toggle also removes the direct signal for Ebow-like sounds. Street price is $180.