The best FREE anti Virus programs are Avast and Avira.
AVG has seen its day as has MSE
Spybot although once a staple for PC installations along with AdAware hasn't been favoured for a long time and Malwarebytes is the standard now.
Its also important to only run 1 malware and 1 AV program at once.
Dont take my word for it though, go have a look here
http://www.av-comparatives.org/
and book mark this place for interesting reports on internet security in general
http://www.grc.com/default.htm