I think this need to be mentioned and i think whoever visits this forum will check out this thread because it has link to the two best programs for Spyware and Adware.

First Program: Ad-aware
With its ability to scan your RAM, Registry, hard drives, and external storage devices for known data mining, advertising, and tracking components, Ad-aware can easily rid your system of these tracking components, allowing you to maintain a higher degree of privacy while you surf the Web
The latest version includes improved Browser Hijacker detection, HOSTS file scanning, smart scan mode which improves speed and has been optimized to detect content at the root, and much more.
Download HERE

Second Program: As mentioned in the second thread, Spybot Search and Destroy.

Spybot - Search & Destroy can detect and remove a multitude of adware files and modules from your computer. Spybot can also clean program and Web usage tracks from your system, which is especially useful if you share your computer with other users.
Version 1.2 adds a variety of new and updated features, including an immunization option that allows you to block many spyware downloads before they get to your computer, and improved detection mechanisms for morphing files.
Download HERE