I recently picked up an EHX micro POG, polyphonic octave generator. Three knobs, source level, sub octave level, and octave above level, you can blend them as you please. I really like the thickness it provides, and it tracks extremely well. With a little distortion before, and a little chorus, envelope, or flange after, it can get, what I would call, gnarly. Still in a very bass-centric, musical fashion. I was especially pleased with the way it integrated in a jam setting. So often we can fiddle around with effects on our own, only to find they don't play well with others. The Micro POG is my favorite new sound.