Here are some anti-spyware products which I reocmmend using:
Spybot Search and Destroy - Spybot S&D is udpated regularly and free to use. They accept donations, but donations are not mandatory to use the software.
Ad-Aware - Another anti-spyware product, this is free for personal use. There is also a commercial version that individuals can buy if they wish to support the product. Business use requires a license.
Malwarebytes - Another anti-malware application, this seems to have gotten good reviews from places like CNet, as well as the help desk staff where I work.
If there are any other anti-spyware products that you think should be listed here, please let me know!