My monitors are usually shelf mounted. I place a 1/2 inch bamboo cutting board on top of the shelf and a thin layer of cork on top of that and then the speaker on top of that. Eats up vibrations very well (lots of truck and bus traffic in Queens).
With my floorstanders I do basically the same thing ... a 1 inch bamboo cutting board on top of the hardwood floor. On top of the cutting board is a 2" thick piece of Auralex acoustic foam. Eats up vibrations equally as well.
Regards, Rich