MailWasher Free is a capable spam filter that uses a variety of techniques to keep your inbox free of spam.
Bayesian algorithms, for instance, analyse incoming emails and quickly learn to distinguish spam from your legitimate emails. External blacklists of known spamming addresses will block more junk. You can create blacklists of your own, add friends email addresses to a white list to ensure their emails will always get through, then build additional customisable filters to mop up any remaining spam.
If you feel like fighting back then integrated SpamCop support makes it easy to report spammers to their providers.
And the program works regardless of the email client and technology you're using: POP3, IMAP, Outlook, Windows Mail, GMail, Hotmail and more.
While this version is free, there's a MailWasher Pro version. This removes the advertising banner, gets you technical support seven days a week, and includes a subscription to the cloud-based FirstAlert! service which automatically blocks known spam messages.