Similar to Symantec above, but with a variation - I love these guys. We used their anti-virus product on Exchange and it was absolutely beautiful. Easy to install, easy to maintain, great features, and it worked perfectly. I loved it.
But... (there is always a but) we decided we wanted to upgrade to their more complex solution and get their anti-spam features in there as well. Essentially meaning that we wanted to give them more money and they would then in turn take it and do whatever it is they do with money. Presumably roll around in it and squealing with glee, I don't know.
But no, their customer service and sales department is awful and they were so rude and condescending that I cut off the transaction and am done with them. I still use them for personal computing needs, the PC-cillin Internet Security product is a good product for the price - but I won't be using them for Enterprise level applications since I don't want to reward their poor service.