MComb

Outstanding comb filter. Comes in the FreeFXBundle and is way more capable that some similar plug-ins that cost twice what it does to upgrade the FreeFXBundle to the pro version.

I love tempo-sync'd modulation FX, and this one lets you set up 4 different poles that can be modulated in a variety of ways. Envelope following, generated, free form, or static if you don't want any movement.

If you have it sitting in your plug-in collection and not checked it out due to not really getting what it's supposed to do, rack it up and start walking through the presets.

I like to put it on drum tracks, makes the whole kit sound like it's rolling across the floor.