Check out
www.mailblocks.com. It's a filtering service that uses a challenge system to validate e-mail...that is, if someone is not in your address book, the system sends them a message they must respond to. If they respond, the message goes through and the sender is added to your address book so they don't have to do that again. Since most spam is automated, there isn't a response and those messages stay in the bin for a few days before being deleted (configurable retention period).
Coupled with your own domain (which I have), you can have your mail automatically routed to Mailblocks, faster than the standard method whereby they periodically check your inbox. The system also features "Trackers," which let you set up disposable e-mail addresses for online registration and other purposes. They have a handy web interface but will also allow you to use regular e-mail clients like Outlook, as long as they can handle IMAP mailboxes.