We love Cloudmark Desktop. It is the best spam filter on the planet and that has been proved by very complicated scientific tests.
The only problem with Cloudmark Desktop is that it only works in Outlook, Outlook Express or Thunderbird. Until now, Vista users who wanted to benefit from the powerful filtering of Cloudmark had to switch their email application over to Thunderbird or Outlook. It would not work in the free Windows Mail (Vista version of Outlook Express).
Well, those days are gone. Cloudmark has released a beta version of Cloudmark Desktop for Windows Mail [1].
I have only installed it once and it was obviously still in Beta, but it still is much better than any other method for filtering junk mail.
Links:
[1] http://www.cloudmark.com/desktop/download/
[2] http://www.yourpcpartner.com/cnet_web_2_0_awards.htm
[3] http://www.yourpcpartner.com/think_twice_your_blame_your_computers_manufacturer_problems.htm