Most of these are available for free from www.filehippo.com:
1) Ad-Aware - run it regularly throw those cookies out! Set it to run daily scans.
2) SpyBot - run it regularly also it's even better than Ad-Aware at getting this crap off your machine. Run at least once a week.
3) SpywareBlaster - pre-emptively blocks all sorts of crap from being installed that people want to install on your machine to hijack it and turn it into their propaganda superhighway to your brain.
4) Run a browser like FireFox with AdBlocker installed and all the ad subscriptions installed. Hides almost all the ads.
https://addons.mozilla.org/en-US/firefox/addon/1865There is also a new style sheet you can load for the new Apple Safari that works in a similar manner to block ads.
5) ZoneAlarm personal (or your favorite firewall) - I used to use Norton but now that I'm officially poor I've stopped using it and have opted for freeware solutions.
6) AVG personal antivirus - I used to use Norton but again this is a free one. Set this to run daily scans.
7) Disable the cookies in your browser and only enable them on particular sites.
8) CCleaner - run this regularly to clean all the crap off your machine including MRU's, cookies, temp files, etc. Run at least once a week.
9) For God's sake NEVER install all those obnoxious "toolbars" on your machine - if they are already installed remove them.. AOL, Yahoo, Google, etc. these things are just there to hijack your PC and turn it into AOL's, Yahoo's, Google's, etc. corporate botnet. They slow your machine down tremendously while feeding your info back to their corporate masters.
10) NEVER ever install Windows Live - this is a hideously intrusive bit of software that is like a toolbar on roids that totally hijacks your PC and attempts to assimilate you and it into the Borg Collective.
11) Get rid of Windows and move to a Mac or better yet a Linux or FreeBSD Box.
12) Watch out for GoogleEarth and other Google programs which install their GoogleUpdater.exe onto your machine. This is another bit of spyware you need to disable the updater service and delete GoogleUpdater.exe from your machine and not allow it to be reinstalled.
13) Remove/disable all the auto-updaters from your machine.
14) Be careful to read the updates and why they are necessary before installing them but don't let a machine sit unpatched for security holes.