CamWorld offers a good list of tips for reducing spam by keeping your main email address hidden.
On this website, I use a tool that creates a new email address daily. This gives readers means to contact me, without requiring me to publish an address that is useful to spammers. (Even if spammers were to harvest this daily address, it would have expired by the time they try to send spam there.)
In the year that I’ve used this approach, I have received 0 spam messages as a result. If you run a public website and have the need to publish a disposable address, you can use this software too; I’ve GPL’d it as part of the Monaural Jerk distribution.
I have plans to enhance this tool. I envision the result as an “address maintenance” system, which gives users the power to easily create throwaway email addresses for every online transaction. The system will track address usage so users can see at a glance whether an address has received any spam. This is targeted for release (free) in the unspecified future.
If you don’t run your own mail server, this sounds like a good solution to the problem. My only gripe about expireit.com is the banner on the front page that reads, “We guarantee you will stop spammers in their tracks in under 60 seconds.” This is terribly misleading. An honest description of their service can be found on the “Long Winded Nutshell” page.
(Thanks to Paul Fatula for the tip on Expireit.)