Actually, the antivirus that run on Windows 7 are:
Kaspersky Lab was first software house to update its product. Kaspersky Antivirus is release as beta, but is stable and full compatible with Windows 7. This beta is free and includes a firewall, a anti-spam filter and other features of KAV 2009.
Symantec, recently, updated Norton Antivirus. This is a free Beta, but I don’t like it because is very unpleasant to use.
AVG updated their software but only professional versions and you have to pay to use.
McAfee is updating their antivirus, but the actual beta has many problems.
Avast and Antivir are, probably, most used free antivirus and fortunately they work without problems on Windows 7.
Personally, I recommend to use KAV until is free and then switch to Avast.
On How to Geek you can find tests of some of these antivirus.
If you want recommend other antivirus write a comment with your motivations.