Musician's Friend has a deal today that drops the price of the Boss DN-2 Dyna Drive Overdrive Pedal down to $29.99. This lists at $163 and sells for $49 at Amazon.

The pedal is highly-rated, and the gist of the effect is this: it reacts to how you play. Play softly and get a soft, clean output. Play heavy and get a heavy, powerful overdrive sound.