Ad-Aware is a very comprehensive adware and spyware removal tool. It is not infallible, but it will find (and clean) most of the "bad" stuff on your computer (other than viruses, but that is another program).
Unfortunately, the free version does not run in the background like an anti-virus program, so the only way it will look for adware or spyware is for you to start up the program and run another search.
I would suggest doing this at least once a month, or anytime you think your computer starts to run slow or you get excessive pop-ups.
After the scan, it will give you a list of what it has found (assuming it found something). Make sure every item is checkmarked by right-clicking on any of the items and selecting "Select All Objects." Then you can click "Next" to clean the items off.
This is usually the first program I run on computers infected with spyware or adware, and I would say this is one of the programs that you need. This program is free for home use, not business use.
Ad-Aware only runs on Microsoft Windows.