In 2002 (or thereabouts) I signed up to beta Messagefire, mooshjan's antispam service. Two years later, it was bought by a slightly larger company, which (from my biased point of view) apparently left the thing in a corner, running on autopilot. I've been using it for my spam filtering ever since, but when the SSL certificates expire, it's time to go elsewhere.
I just shuffled my mail flow around so that spam filtering is being done by Gmail instead.
*tips hat to mooshjan*