Free Spyware, Adware, Privacy Tools
This rookit revealer freeware from sysinternals detects persistent rootkits on windows 4.0 and higher.
Malware Destroyer freeware
Malware Destroyer is a malware removal tool that claims a new and faster scanning engine. According to the website it takes only about 10 seconds to search for various types of malware including adware, spyware, dialers, etc.
HijackThis examines certain key areas of the Registry and Hard Drive and lists their contents. These are areas which are used by both legitimate programmers and hijackers. It's up to you to decide what should be removed.
Spybot is my favorite freeware removal tool for spyware. It features removal of threats by shredding them, backups of every removed problem and a whole lot more. Spybot is freeware for Windows 95/98/Me/NT/2000/XP.
Ad-Aware Free Antivirus+
Formerly just an adware and spyware remover, this now includes anti-virus in the free editions, which naturally has some limitations.
SpywareBlaster doesn't scan and clean for spyware, but it prevents it from ever being installed by preventing the downloading of certain ActiveX controls. It also has a system snapshot utility that allows you to detect changes and undo them.
Keylogger Hunter 1.0
Utility that attempts to detect the activity of keyboard monitoring programs running on your PC. Windows freeware.
The new version of the popular Google Toolbar features a handy popup blocker. If you use the PageRank feature it will send information about the pages that you are viewing to Google, but you can disable this feature.
XP-AntiSpy is a little utility that lets you disable some built-in update and authentication features in WindowsXP.