I'm looking for some feet for my case but i also thought i could put some on my laptop. What do you think of these; other ideas always welcome. http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWAX:IT&item=260323888061
Those look like they will work just fine. http://www.frozencpu.com/cat/l3/g43/c12/s34/list/p1/Case_Parts-OEM-Misc_Case_Parts-CastersFeet-Page1.html FrozenCPU has some in different colors if you are interested.
For small feet have a look in Wilko, they have a decent selection. For a tower case the 13mm ebay ones look a bit small, I've used the rubber door stops you can buy (though I got mine from Woolies). And have a look at Maplins' range.