Rubber grommets are one of the best things to happen to cases in quite some time. While they are small and inexpensive, they serve two purposes: they help keep your case quiet and they make your case look more professional and finished.
Originally, these were just used in fan mounting, but now they have started to be used in drive cages and elsewhere.
Specs: 4 to a pack in one plastic bag. Black Rubber Washers.