There are four very good spyware removal programs that I highly recommend listed in order of personal experience and ability to find the hard to remove adware / scumware. For best results it is recommended that you use all four removal programs to ensure total protection of your computer.

Spy Sweeper From Webroot
This spyware eliminator found the most spyware and adware out of all the products I tested. It comes with a free 14 day fully functional trial and free online spyware detection. While the full program costs $29.95 I feel its well worth the price to keep your system clean and free of nasty pests.
Click Here To Download Spy Sweeper

Adaware From Lavasoft
Ad Aware is a very powerful tool from the good folks at Lavasoft. The program is very comprehensive and best of all totally free for personal use. It finds most of the common spyware programs but ive found that Spy Sweeper seems to update more frequently as well as offer better support.
Click Here To Download Adaware

Spybot Search And Destroy
Spybot S&D is a favorite spyware removal program for many. It is very comprehensive and updated often with the newest known bugs, trojans, dialers, etc. It is a free program however we recommend a donation as the developer lives on the monies raised.
Click Here Download Spybot Search and Destroy

Microsoft Giant Anti Spyware Beta Microsoft recently purchased a company named Giant and is now releasing its own version of the software free to windows users. While I have not personally used the software I have heard very good reviews from peers who claim that its very robust. The price is free however you may need to verify your windows serial number to download.
Click Here To Download Microsoft Anti Spyware Beta

I hope the programs above are helpful and if you need any more information or resources here are a few good websites to help out.