One of the most amazing products I have seen in a long time is the Proofpoint spam filterieng appliance. I've been one of the first to use it before we roll it out to our user base, and I have to say that the result has been amazing. I literally get zero spam now that I am using the appliance to filter my mail.
It's actually a pretty novel concept as far as spam filtering goes. All mail passes through the Proofpoint appliance, which lives upstream of the mail server. The appliance grabs any messages it considers to be spam and passes the rest along to your inbox. Then, at some set interval (e.g. daily), you get a "spam digest," an email message delivered to your inbox listing all of the messages (subject line, sender, etc.) that the appliance caught. Next to each message listed in the digest, there are links which allow you to take an action on that specific message. For example, you can click a link to "release" a message, which will tell Proofpoint to let go of the message and deliver it to your inbox. You can safelist the sender of that message so that sender's messages will never be marked as spam again.
In addition to the digest, you can log into the web interface anytime and see the messages that Proofpoint has caught. From the web UI, you can perform any of the actions you can from the digest.
This model is a really nice way of dealing with spam, but the best part of this product is really its accuracy. I have experienced very few false positives and have been very satisfied with the product overall. I can't wait to roll this out to our users; they are going to love it.