Ad-aware 6 was the previous version of Ad-aware and is no longer being updated by Lavasoft.  Their website encourages everyone to update their system to the Ad-aware SE version.

Spybot Search & Destroy 1.3 is another excellent free spyware detection and removal program written by Patrick Kolla.  It has a feature called 'Immunize' that basically blocks a number of bad websites from running anything on your pc.  It is also updated rather frequently, so keep your includes and your check library up-to-date.  For assistance, see this tutorial.

SpywareBlaster 3.2 is a free spyware blocker that 'prevents the install of many unwanted spyware programs, blocks spyware/tracking cookies, and restricts the actions of potentially dangerous sites'.  It is designed by Javacool Software.  Make sure that you keep it up-to-date using the 'Check for Updates' button under the 'Updates' tab.  For assistance, see this tutorial.

CWShredder 2.1 is a program written by a college student from the Netherlands named Merijn Bellekom and is now owned and maintained by InterMute.  It is specially designed to fight against a strain of spyware programs based on the CoolWebSearch model.  It is very small, runs very quickly, and is good at what it does.  I recommend running this before running Ad-aware or Spybot as a first measure.

HijackThis is another program by Merijn.  It is very powerful in the right hands but you can screw things up pretty badly if you are not sure of what you are doing.  Warning: It is NOT for amateurs.  If you do not have an advanced knowledge of computers you should NOT fix anything without consulting experts.  A tutorial on how to use this program is available, but I would recommend that you only do the parts that generate the reports, post the HJT report logs to one of these forums, and let the experts tell you what to remove.

BHODemon protects you from unknown Browser Helper Objects (BHOs), by letting you enable/disable them individually.  BHOs are a very powerful entity on your pc.  There is no restriction on what a BHO can do, it can do anything any other program can do: read or write (or delete) anything on your system so it is important to be sure of what BHOs you have on there and what they are doing.

WinPatrol 7.0 uses a different approach to preventing spyware and other unwanted items from infecting your machine.  'Scotty the Windows Watchdog' takes a snapshot of critical system resources and immediately alerts you whenever something changes.

SpywareGuard 2.2 is another program written by Javacool Software.  It provides real-time protection, much like an anti-virus program does, but for spyware.  It strives to block spyware executables before they run, protect against downloading spyware files, and stop browser hijackers in real-time.