NANO Antivirus is a free antivirus from an up-and-coming security firm. It provides a whole host of features, from automatic scanning of CDs and USB drives, to express scanning, and many more that both home and small business users can use.
Built to be used
It's hard to overstate how many features NANO Antivirus has. You can schedule scans and updates, or get updates incrementally: basic functionality made amazing. Aside from that, it provides web browser and operating system level security. It also adjusts to your current power usage. The only drawback to NANO is that it can be a bit power-hungry: it requires Windows XP SP3 or later, which is simply enough, but it also requires a machine running at 2GHz or better, and quite a bit of RAM. For some offices, this may be difficult to swallow. On a machine that meets the requirements, though, NANO does run very unobtrusively.
At the end of the day
NANO Antivirus is a fantastic solution for home antivirus use and a serviceable one for professional use. It's easy to expect that over time, it'll perform better in small business contexts, especially as the performance improves and its antivirus lab grows. In the meantime, it's worth checking out if you're looking for an alternative to your current antivirus, or for a new one to go with a new computer.