Become hard to find.

This is probably the single best and most effective method of warding off the spammers. If you don't give out your primary email address except to trusted friends etc. and organizations you can keep a nice clean mailbox.
The best way to do this is to sign for the free online mail service providers like hotmail and yahoo. You can even get disposable email addresses that disappear on their own. Use these addresses when you think you may be exposed to a junk emailer.

When you do start getting too much spam to any of the free accounts just cancel it and get another one. You should also use a disposable account if you post messages to the Internet forums just to be sure. Spammers often use software that combs newsgroups for email addresses.