I go with Avast free and Malwarebytes pro, with Spybot S&D as backup (handy for it's host file blocking features), I used to like Webroot's package on Vista a few years back but haven't tried that with Windows 7. I've also tried Kasperski 2010 with windows 7 (won a free licence for a year) and it was such a terrible experience that I ditched it after a month, largely to the very cumbersome options which are frankly bordering on silly for an average joe to understand, caused me no end of hassles trying to use its built in firewall, such a shame as the detection and blocking rates seemed superb.