Anti-Virus
A good anti-virus will monitor all data traffic whether from the internet, your hard drive, e-mail, floppy disks, CD's, flash drives, etc. It will update itself regularly and should scan for existing infected files on at least a weekly basis. Avoid running two or more active A-V programs as they might clash with one another.

Anti-Spyware
Spyware is primarily used for marketing, whether to directly send you advertising or to gather information about your habits which might then be used to better target future ads to you. It slows your system down and serves little purpose to you or your computer. A manual scanner solution works fine but must be updated and run regularly to help.

Firewall
A firewall monitors all traffic between your computer and your network/internet. It prevents hackers from gaining directly access to your system. The best firewall is a hardware-based firewall which are included in most routers. Most firewall attacks are thwarted at the router before they ever reach your computer.

Anti-Spam
These products try to stem the ever-increasing flow of junk mail, or spam, that you receive. Because there are so many different e-mail programs, there is no single solution to filter the spam from the good e-mail. If you use an on-line web-based e-mail reader, your service may have options to turn on a Spam Filter of some sort; use it.