MBAM has a free version and is very good. Paid (resident) version $25~.
Superantispyware (referenced above) is also very good, Paid version ~$20.
These are, I believe, one time lifetime fees.
The latest version of AdAware, (to use a highly technical term) sucks.
Can find and remove tracking cookies. Nice looking GUI. Probably why it's popular. After all, the GUI is the most important part of a program.
(Some folk actually seem to think that.)
Other pretty good scanner/cleaners include, Asquared, Spybot, and if a bit more expert, SREng by KZTechs, AVZ antiviral toolkit by z-oleg.com (yes it's Russian, and so is the website) and Radix by USEC.
Seen quite a few horror stories on the www about the new AVG8 "suite", but also must balance that by saying a few folk seem very happy with it.