I went on a search recently for the top rated free antivirus and spyware software. I found hundreds of free or free trial software options, but only a few stand out.

Avast 4 Home Edition: Scans for viruses, worms and Trojans.

Spybot Search and Destroy:  Detects and removes spyware.

I currently use both these products and am very happy. The Avast anti-virus software catches everything. I have not had issues with spyware, or any type of virus since.