I have used the free Ad-aware and free shareware, Spybot S & D, in conjunction with each other (seems to be the most oft recommended method of dealing with spyware problems from most people 'in the know'). And was quite happy with the results, doind cleanup scans several times a week. after many months of such, I decided to purchase, online, the Plus version of Ad-aware, with it being proactive in keeping the garbage off, rather than rective and cleaning the mess up each week, or several times a week. Since installing the Ad-aware Plus, abouut 3 weeks or month ago, I have not had one spyware find residency on my PC. I have run Ad-aware scans a number of times, along with Spybot S & D (updated to their new ver 1.3 about a week ago) and neither ever come up with any. I like it.
Along with Ad-aware, I use Norton and Panda antivirus in conjunction, daily updates on both, Zone-Alarm firewall (great new version 5 out now) and hardware router firewall. For email cleaning, I use Mailwasher Pro, another wonderful program.