This list has been recently updated and is from my blog post found here.

• Audio Player - iTunes
  There are many other very high quality audio players out there, but for sheer use of use and features I am using iTunes right now. Plus stay tuned for a 'how-to' post focused on organizing your music collection for tips on adding album artwork, renaming your files, sorting your music, and creating custome playlists using iTunes. (Note, if you need to move files from your iPod to your computer, I recommend using EphPod)
• BitTorrent Client - µTorrent
  If you know what BitTorrent is, you need this client program.
  
• CD/DVD Burner - CDBurnerXP Pro
  Nero is great, but they charge for it... this program will take care of 99% of your CD and DVD burning needs at no cost.
  
• Chat - www.meebo.com,
  I can not say enough about meebo. This is a great web application that allows you to sign onto the instant messaging sides of AOL, MSN, Yahoo, Google, ICQ and Jabber. Because it is web based you don't need to download any programs and you can log on from anywhere. Create a user name with meebo and you don't even need to remember your screen name and password for each of your accounts. Words can not describe how well this site works, unless you are using Internet Explorer, I have heard its performance is a bit more stellar with Firefox. Chat runners up: Gaim or Trillian (if you need to download a program onto your computer to feel like you are really chatting)
  
• Compression Tools - ZipGenius
  If you have never needed a program to zip and unzip files, don't worry about this one... but if you need create an archive or get into a .rar file every once and awhile, this is the program for you.
• Desktop Background Manager - Wallpaper Master
  If you like the background of your desktop to change with some regularity, check out Wallpaper Master. And if you need some wallpapers, go to InterfaceLift.
  
• Earth Viewer - Google Earth
  If you have yet to see Google Earth in action stop reading this now and download it -- you will be amazed at what you can see.
  
• Email - www.gmail.com, Thunderbird
  Gmail is wonderful -- even if you use another web based mail service such as those provided by Yahoo! or Microsoft, you have Google to thank for the improvements they have been forced to make over the past couple years. If you need to have a local mail client on your computer, Thunderbird is a great alternative to Outlook.
  
• Image Editing - Paint.NET
  If you need something better than what Microsoft gives you with your copy of Windows to edit images, but you are not quite ready for Photoshop, Paint.NET is the way to go.
  
• Image Viewer - Picasa
  If you have a digital camera, Picasa is here to save you from the crappy software they gave you with your camera. Uninstall the program that came with your camera and use this instead.
• Keyboard Computer Navigation - Launchy
  Faster with the keyboard than with the the mouse? Check out Launchy, a program that can access your internet favorites, your start menu programs, and many other things, without ever having to remove your hands from the keyboard. My favorite feature is the calculator... check it out!
  
• Office Suite - OpenOffice.org
  Ready for the best kept secret on the internet? Here it is: Chances are, you don't need Microsoft Office. OpenOffice.org can open, create, and edit Microsoft Office files in an environment very similar to the Microsoft products. Check it out, I almost guarantee it will fit your needs... I repeat you can open, create, and edit Microsoft Office files.
  
• PDF Utilities - Acrobat Reader, PrimoPDF
  Acrobat Reader is pretty much a necessary evil. They did just come out with their new version (8), so click the link above and go get it... much more useful, however, is PrimoPDF. This program adds a virtual printer to your list of printers. When you select the PrimoPDF printer instead of you HP LaserJetMate XL VI24, the program simply creates a PDF file that you can then email, save, or print. It is a great way to save trees and create PDFs (which, among other things, can have great security features).
  
• Phone - Skype
  If you have yet to try Skype it is worth checking out. Everyone has a different opinion of internet phone, but you should at least know how the rest of the world is communicating (Skype is very popular in Europe and Asia).
  
• Video Player and Codecs - K-Lite Codec Pack
  If you have ever downloaded a video file that would not play on your computer it is because you did not have the proper codec. Once you download the above "pack" you will be able to watch the newest video of Bob Sagget telling you about his tryst with Kimmy Gibbler.