You should already be forwarding your Spam email to SpamCop. (After all, if you just delete it and ignore it, you're part of the problem. And don't even think about replying to the bogus "opt-out" email address listed in the Spam.)
Often you do need to give a valid email address at some websites (leaving you open to Spam). Along comes Mailexpire.com, which lets you generate "temporary" forwarding emails, which will expire after a set length of time (hours, days, months). Bookmark it now.