The free version of AVG anti-virus is one of my favorites. It performs as well as most pricey programs. It is easy to use, and is also easy on system resources. It is available at http://free.grisoft.com . AVG also has a Free Anti-Spyware program.
The only drawback to using these free programs from AVG is that there is no tech support. Most of the time you won't need it, but if you do, you will have to cough up the money for the paid version. These free AVG programs are available for single computer use for the home and non-commercial use. If you have more than one computer at home or have a business, you will have to purchase a paid version.
If AVG doesn't suit you for some reason, you might want to try Avast, which is another free anti-virus program that can be downloaded at the Avast Website.While I like AVG a little better, this program is also suitable. The same rules apply here. It is free for a single computer users for home and non-commercial use.