ad-aware

With its ability to comprehensively scan your memory, registry, hard, removable and optical drives for known data mining, aggressive advertising, and tracking components, Ad-aware will provide the user with the confidence to surf the Internet knowing that their privacy will remain intact.

spybot

Perhaps the most complete freeware tool is Spybot Search and Destroy. This not only sniffs out and removes any hidden fiends, it can also immunize your system against over 400 different spies.
Regularly updated data files help keep you protected, and the package even supports over 30 languages.

spywareblaster

SpywareBlaster prevents the installation of ActiveX-based spyware, adware, browser hijackers, dialers, and other potentially unwanted software.
It blocks spyware/tracking cookies in Internet Explorer and Mozilla/Firefox.
It restricts the actions of potentially unwanted sites in Internet Explorer.

spywareguard

SpywareGuard provides a real-time protection solution against spyware that is a great addition to SpywareBlaster's protection method.
An anti-virus program scans files before you open them and prevents execution if a virus is detected - SpywareGuard does the same thing, but for spyware! And you can easily have an anti-virus program running alongside SpywareGuard
SpywareGuard now also features Download Protection and Browser Hijacking Protection!

hostman file manager

Hostman is a freeware application that lets you manage your Hosts file with ease.
Windows Host file prevents spyware going out from your pc to the intended spy web sites.
The spyware is diverted to a non existent web site address instead.

zoned-out file manager

Zoned-Out is a freeware application that lets you manage your zone file with ease.
The Windows zone file prevents a web site from opening in your browser if that web site is listed.