There are dozens of good anti-spyware programs on the market, but I'm going to highlight a few that I prefer because they are free and easy to use.
SpywareBlaster doesn't scan and clean for spyware - it prevents it from ever being installed. It will also stop malware from communicating with its host server. This helps to stop popups and malware from functioning and further spreading the infections.
Malwarebytes' Anti-Malware can detect and remove malware that even the most well known anti-virus and anti-malware applications fail to detect. Malwarebytes' Anti-Malware monitors every process and stops malicious processes before they even start.
SUPERAntiSpyware features a highly advanced Real-Time Protection to ensure protection from installation or re-installation of potential threats as you surf the Internet. Used in conjunction with their First Chance Prevention and Registry Protection, your computer is protected from thousands of threats that attempt to infect and infiltrate your system at startup or while shutting down your system.
Spybot S&D searches your hard drive for so-called spy- or adbots; that is, little modules that are responsible for the ads many programs display. Many of these modules also transmit information, including your surfing behavior on the Internet and possibly your personal information. If it finds these modules, it can remove them. In most cases your computer still runs fine after removing the spyware/adware.
Here you can see the feature that allows you to immunize important files and folders:
And one of my favorite things about this program- once it finds infections, it gives you valuable information about them.
No matter which program(s) you choose for spyware protection, make sure you update and scan often (at least weekly). Severe spyware infections can require professional service to be completely removed.