I'm actually in the same boat you are right now. We run Exchange and are using FrontBridge as a 3rd party spam filtering service...but it doesn't work very well. I've looked at numerous 3rd party appliances recently (Barracuda, St. Bernard ePrism, Sonic Wall, etc.), however we're probably going to be going with a Cisco ASA 5500 series appliance in 07' and there is a module for it which does spam filtering, so that's probably what we'll end up using.