I think Postini is one of the best anti-virus and anit-spam solutions for corporate e-mail -- essentially all e-mail filters through Postini's servers and anything that is caught in the Postini filter stays on the Postini server until the user logs onto the Postini site and decides what to do with the e-mail; all viruses are deleted/fixed by Postini. Postini has a bunch of other features for IM, mobile e-mail access, e-mail retention and storage, and other online communication control tools.
Google announced today on the Google blog that they have purchased Postini, which adds much more strength to the Google Mail and IM products. Further, as I point out above and the Google blog points out, Postini is a hosted solution, making it very similar to all of the Google offerings.
Pretty cool -- I'll be interested to see if many of the Postini services become free.
Link -- Google Blog about Postini
Link -- Postini