AmazingNoises make some very nice free Max for Live devices.

This is their GliderVerb, a "reverberator with glissandos". It takes the dopplering noise you get when changing room size and turns it into a feature.

I racked it on Eric Beam's phase canceled frequency divider, downloadable here.

Nice to put on kit drums: you can mangle the hats while letting the kick go through, or vice versa.