These are highly recommended AntiVirus and spyware apps and they are all free...
Remember though only install one AV,as more than one on your computer will make them clash, but you can install all the spyware apps...
Anti-virus:
avast! AVG free Avira Antivir Antispyware etc: ad-ware __(FREE) Spybot - Search & Destroy __(FREE) AVG Antispyware (formerly Ewido)