AVG free is a good program, the paid version is better only in that it will auto-update, and the freeware version is a manual update. Both work very well for VIRUSES.
I capitalize that because most problems that are blamed on viruses, are not viruses, they are malware or spyware or trojans.
You should always run at least one anti-spyware program, along with your anti-virus.
I use Spybot Search and Destroy along with the AVG free. It is shareware, but you can download it free, and they ask for a donation to support the web site, rather than a fixed price.
I have been able to download files, even from such highly infected sites as Limewire and Bearshare, and have never been infected, as between the two programs, they have stopped any infected downloads before they could damage my machine.
WARNING: Never install a second anti-virus program, without first removing the one you have already installed. Anti-virus programs can fight each other and cause very unpredictable results.
You CAN have more than one anti-spyware program running at once, but you could end up tell two, three or more programs to allow a change you are making to happen when the detect a new installation or change to your files.