Browsers
Firefox- Personally I stopped using it after it would give me BSOD in 3D apps after opening it, was fixed in later versions but I couldn't be bothered. I've been running IE7 since then and I like it very much.
Anti Virus
AVG and/or Avast! - Free for personal use, used together give you a good secure net.
Spybot Search and Destroy - Free, constantly updated and works well!
Malwarebytes Anti Malware - Kind of like Spybot, used it on a few occasions to get me out of trouble
Video
Windows Media Player - Use with a complete codec pack and it's pretty good, as a second I use FLV player and Realplayer as a third.
Audio
Windows Media Player, again you can get codecs for the wierd files and it just generally works well. Otherwise I'd use Winamp but I'm not for migrating to new software
OS
Windows XP - Good for the all round home user/gamer, alot of products availible
Mac - Haven't used it myself, but I hear it's very good for the designers/artists among us, and you can run Windows on it just as well as a Windows machine.
Misc
Adobe Photoshop - Clearly.
Some form of Torrenting program, Bitlord works for me (although I'm not promoting the use of them)
Microsoft Office - for the work stuff.
WinRAR - An essential
MSN - Obviously
Xfire - Track your gaming!
Steam - A must for anyone who plays HL or anything else that's on Steam
Some HD cleaner - Don't use any myself but you should use one, really.
Games - Ones you like, weirdly enough.