Kaspersky Antivirus. It warns you when a virus is detected. It goes crazy-it starts flashing VIRUS VIRUS and you just have to delete it My friend has it ad she said that with Kaspersky, she had no virus ;O You have to buy this one.
its all upto you.. avg, avira & avast free versions are ok for normal users.. if you surf internet a lot then get antivirus with firewall (paid versions)or free antivirus with other firewall programs..
for protecting from Flash drives use USB Disk security,, its a small program & worth a lot better than paid antivirus in many situations..more than that you must have some knowledge with security issues like avoiding pirated softwares with keygen may have trojan, unwanted sites( try using firefox with addons like No scripts,WOT like that)
Download & Install the following 3 freewares. It forms a free complete security suite for your system!
1. Avira Anvivir - http://www.free-av.com/en/download/index.html .
Avira has very good internet security, real time updates, great overall protection.