Trend Micro, mentioned previously, is one of the leading corporate level brands. I've used it on a number of installations (small, large and gov.) to great effect. Hotmail now uses them for their built-in scanning solution as well. That's a huge client, as you well know. Also as mentioned, it is not free, but it is good. It is primarily for email scanning though... not really a full virus program.
I prefer for my own machines a clean install of Symantec Anti-Virus Corporate. The Professional (home-user) version is good but the corporate version is the slimmed down on flash / heavy on useful version.
Either way, the anti-virus program is still very good and well deserving of the industry leader that it gained years ago. You cannot compare the Internet Security to the Anti-Virus program as the I.S.'s problem is the all-in-one launcher and attempt to make it dummy proof. The combo packs are bloats-ville (I.S., System Works, etc.). Plain Symantec Anti-virus is the way to go.