I filter all my e-mail via an online spam filter (there is a 14-day free trial if you want to test it out). I've been using it for just over a year now, and it has blocked 37,646 emails (80% of my e-mail). Cost is £2.50 per month (or cheaper if you pay annually).
It works by filtering out KNOWN spam messages, plus also using a WHITELIST (a list of e-mail addresses which you trust). If you get a message from someone you trust (on your whitelist), the message comes straight through. If the message comes from a known spammer... it gets deleted (held for 30 days, so you can search through deleted messages, should it have deleted something by mistake. I've found it very reliable, unusual for a message to be marked as SPAM when in fact it was a real message).
When the system does not know if it's spam or not... the message gets held in a queue, and you get asked to confirm if you wish to accept the message once, or every time from that sender. You can read a text-only version of the message, if you are unsure if you want to trust based just on Subject Line and E-mail address. The system learns what you will, and won't trust, thus it gets better the longer you use it.
It will work with any POP3 e-mail system. What it does, is it checks your e-mail... and you set your e-mail software to check your mail at the spam filter. I found it easy to setup.