I've been trying out different programs so I thought I'd compile a list of the best software I've used for Windows. All software listed are freeware and are easily available via www.download.com :
Antivirus: There has been a lot of debate on this issue recently, but in my personal experience I find Avast! Antivirus to be the best. Its updated multiple times a day, has a number of different protection modules which check your hard disk, websites, internet email, outlook email, network from attacks, and you can also enable a boot scanner to run a scan at startup.
Spyware: I found Trend Micro HijackThis to be the best spyware removal tool. A word of warning though, it only lists potential spyware and does not offer any recommendations as to what files/registry entries you should 'fix' (namely, delete) from your system. Use it with extreme caution to avoid killing your Windows install.
Registry Repair: I use two software, GlarySoft Registry Repair and TweakNow RegCleaner. Both seem to catch different registry problems and are almost fully automated. Excellent software!
PDF viewer: Sure Adobe Acrobat Reader does the job, but its slow, hogs system resources and takes forever to startup. Try Foxit PDF Reader. Its fast, allows opening of multiple PDFs as tabs in the same reader window and you can also fill and save PDF forms etc. If I may venture an analogy, Adobe vs Foxit is like Internet Explorer vs Firefox!
Compression: I use WinRAR to deal with compressed files. It can handle all sorts of compression types one usually sees, and I've never had a problem with it after using it for many years.
Video: Again, something which has been discussed to death. But I have yet to use a better media player than VLC!
Hope you guys find this useful!