We're looking for an email virus scanner to run on our Exchange 2010 server (2 client access servers, 2 DB servers in a DAG). We're currently using Kaspersky for our client AV and have been happy with its performance so far.
For Exchange we'd want something lean, simple, and non-intrusive. We run a virus scanner on our email gateway (Sonicwall) so this would server as a second line of defense and for any internal emails.
Also, it would be preferred to have the anti virus software run on the Exchange Client Access or Hub Transport server instead of the database servers, though I don't know how possible/realistic that is.