The best of breed programs constantly change as new and better ones are created -or- old reliable ones are ruined by creeping elegance and bloat. My current preferences are:
Anti-virus - AVAST! (free) -
http://www.avast.com/free-antivirus-download
Free - not such a resource hog - very effective - excellent range of controls and settings
Anti-spyware - Superantispyware (free) -
http://www.superantispyware.com/download.html
Much less of a resource hog than others - effective
Anti-malware - WinPatrol (free) -
http://www.winpatrol.com/download.html
Great program - will pretty much prevent changes to your system by rogue programs, websites, etc. Have used it for years. Vista and 7 have sort of an equivalent built in.
Disk Defrag - Auslogics (free) -
http://www.auslogics.com/en/software/disk-defrag/download/
The Windows built-in defrag sucks. This one is better and free. Run every couple of weeks or so, depending on how many files are saved, changed, erased, etc.
Junk and Registry cleaner (free) - Ccleaner -
http://www.piriform.com/ccleaner
This will clean up junk files and registry errors. Will usually help system performance. should be run monthly or even weekly on a heavily used system.
There seems to be a lot of suspicion about free programs and sometimes justified. But frequently, companies that make first class programs will offer free home versions just to acquaint people with their product and perhaps those people will buy the professional version (usually with more support) for their business.
I have used some of these for years without any problems. Some are newer. Norton anti-virus was the best and bloated up to unusable. McAfee became the choice, then they went crazy with protection and up-selling. AVG had a great product and a free version, but went nuts with up-selling and it became a resource hog. So currently AVAST! is my preference... Tomorrow, who knows.....