I second the SRA recommendation. Yes, they can be costly, but IMO there is no better isolation device on the planet. I have them under every component in my system, and the difference they've made in the sound quality is nothing short of astounding. If you can afford them, and don't want to settle for anything less than the very best, check out SRA. They're worth every penny.
What's under your amp?
Interested in hearing the importance (or not) of isolation platforms for amps. Check my system, you'll see I've got my Cary's sitting on top of my cabinet, which is a custom piece made of solid cherry. Very solid, but I'm wondering if maybe the cabinet is introducing vibrations up into the amps, and maybe I could use some help from a platform?