If you want free I would suggest Avast which scans as a screen saver so while you are away from your system its doing something usefull.. its also free and better than AVG

and I would use comodo firewall which is much more flexible and better than Microsofts offering and is also free

Spybot search and destroy is a reasonable free spyware protection

a lot of protection can be obtained with a great hosts file as well imho