PowerCurser is an free downloadable Flash Toolkit that allows you to create touchable interfaces.  It simulates stickiness, volume, pressure and roughness.  What is interesting about it is that it doesn't use any sort of physical feedback. Their approach is to use graphics and alter the way the curser responds to create the illusion of touch.  Essentially, your brain is doing all the work by taking in the visual stimuli, filling in the gaps, and creating the perception of touch.