I have used Inboxer for over three months as a test for some clients. It is a superb spam filter and learns very quickly. I have set it to check an account that is deliberately made available to advertising and a few friends. In all the time on trial it has never sent a serious email straight to spam but holds them in a review file. Once the message has been allowed it learns immediately/ You can set Inboxer to delete spam automatically or let you review it.
The only downside is that it will only work in Outlook not express. It now deletes all the spam/advertising without me reviewing any of it.