Ad-aware In our opinion, it's the best software available to wipe all the spyware on your machine. With it's adware auto alert software, which runs in your system tray, keeps you informed of any changes being made to your registry or any suspicious process running.
Spybot Search & Destroy Excellent free software to remove spyware from your computer and it comes with many useful features. RECOMMENDED!
Scumware.com Very good page for general information about Spyware, with some useful information on how to manually remove some of the worst spyware.
Spyware Guide Spyware Guide not only offers links to anti-spyware software but also provides lists of companies distributing spyware, and lists of software and applications known to contain spyware.
Security at Home: Fight Spyware The Microsoft Security center provides detailed information on spyware and tips and information on how to find and remove spyware from your system.