For the next 24 hours, tiomiala@jetable.com will point to my real email address via this free service. A cool idea. Of course, its basic premise is one of trust—you don't trust whom you would give the dispossable address to or the venue you're using to communicate it. Therefore, you need to trust the provider of the service, of which we don't really know anything about. But I guess I got over that.
See also: Mailinator, which let's you make up an address on the spot, which seems handier. Also, their tagline: "It's like flicking a BOOGER at spam." (At first, I read that as "blogger," but booger is much funnier." (via Bay via Joel)
Addendum: Amit has compiled a list of such services on Spamotomy.