AVG 8.0 Free released, now with protection from spyware
AVG Free 8 doesn't have all of the features you get in the commercial version of the application. There's no rootkit protection or linkscanner. And there's no email or instant messaging integration. For those features you'll have to shell out $35 or $55 for the standard or "internet security" versions. But as freeware antivirus applications go, AVG is packed with features like real-time protection, daily updates, and complete system scans at regularly scheduled intervals.
Update: As several readers have pointed out in the comments, when you install AVG Free 8, you will likely find a bunch of advanced features like linkscanning and email protection. The AVG web site has a comparison chart showing that these features are included in the commercial version but not the free version. It's not clear if Grisoft is including free trials of these functions or if the chart is wrong.