I often use the small, round, clear feet made of silicon rubber, self-adhesive. It works suprisingly well; I have 4 feet on my cutting board in the kitchen, and they have never fallen off in about 4 years of washing, occasional bleaching, etc.
You can buy 'em anywhere (Zellers, hardware stores, Wall Mart, etc) 8 for about $2. Look in housewares or hardware.
They will come off if you don't clean the surface first; and you can knock them off (because they stick out a bit) if you're careless. Still, it's simple enough to replace one.
Radio Shack has quite a good selection of "little rubber feet" that have an adhesive side. Most other electronics hobby shops should also have something similar. Carpet underlay is available with adhesive backing and works like a hot damn. The carpet place will probably GIVE you a small piece for free if you ask nicely.
OR....you could buy a small scrap of silicon rubber, or neoprene or something...carve little discs out of it and fasten it to whatever device you have with a bit of "jewler's goop" or a hot glue gun or superglue or even a small wad of half-solidified snot, for that matter.
There are LOTS of possibilities. Use your imagination.