I just got a nifty listing of temporary email services from a resource called Sizlopedia. Rather than list them individually, here's the list.
Mailexpire lets you have a lifespan of an email address from 12 hours to 3 months.
Spambox from 30 minutes to a year
Tempomail (French and English versions)
SpamBully (download product that works with Outlook and Outlook Express) Commercial
There are also another 12 over at my 'I want to...' site that you might want to take a look at - Email - Disposable addresses