My favourites are the Klon Centaur overdrive, my old Jem Cry Baby, an original MXR Phase 100, my newest, which is the HBE Twilight Drive (only mine is white not black!), and my all time favourite, the Boss DF-2 Super Distortion & Feedbacker.
The Klon has the least impact on tone I ever heard in a pedal, but it still drives the amp as if you cranked it. The old Cry Baby has a tone that seems to be missing from the newer pedals, it seems to have more lower mids. The Phase 100 has the phase 90 sound with 3 other settings, none of which I ever use!!
TO already gave you the description of the Twilight Drive.
The DF-2 is basically a DS-1 with a feedback circuit. You can set when the harmonic comes in on the feedback and the balance of feedback to distortion. The name was changed (at DiMarzio's request), to Super Feedbacker & Distortion, but the pedal is the same. You hold down the switch for the feedback feature.
Mind you with the Klon and Twilight drive, I can get feedback at pretty low volumes anyway!