Don't Post Your E-Mail Address to the World
Don't give your e-mail address on Websites, forums, or newsgroups. The Spammers have web crawlers that look for e-mail addresses posted to the internet. Most web forums nowadays will not include your e-mail address with every post, but some still do. So that humans can still contact you, there are easy ways to allow humans to read your address, but not the spam machines. For instance, if you write your e-mail address as "help at crisp net" rather than "help@crisp.net", a human will still know what your e-mail is, but the spam crawlers won't.

Use a Local Filter
Most E-Mail clients nowadays have some level of e-mail filtering built-in. Many of them are a bit arcane, but quite usable. Outlook Express, for instance, has a reasonably intelligible rules-based system for sorting your incoming e-mail, including spam. At some point, I'll write up some pointers for this. However, rules-based filtering is rather tedious and eventually futile, which leads us to:

Bayesian Filtering
Bayesian filtering, besides being difficult to pronounce, is a "learning" mail filter. Essentially, as mail comes in, you mark e-mails as "Spam" or "Not Spam". Pretty soon, the mail program will be able to recognize what is or isn't spam, and quickly filter it out for you. The best part is that it's constantly updating, you just mark any messages that are mistakenly labeled, and the filter learns. Currently, Mozilla and Netscape's browser's e-mail clients support Bayesian filtering, and I've found two plug-ins for MS Outlook that implement Bayesian Filtering, Outlook-Spam-Filter and SpamBayes. CrispNet recommends everyone use Mozilla for browsing the web and reading their e-mail. It's a great browser and doesn't have all those ugly security hassles that IE enjoys.