I'm using the registered version of Mailwasher Free
http://www.mailwasher.net/ (registration gets rid of the ads) and couldn't live without it. MailWasher deletes email directly off your internet providers server before it is downloaded. Simple, fast and just works.
The set of filters available from
http://www.w5hq.com/MailWasher/MailWasherFilters.txt works well and you can write your own additional filters to suit your needs.
Mailwasher Pro may be even better.