Here is a list of useful freebies I've found. These range from fun to functional, with a few pointless wastes of time in there if you need to put your brain in neutral for a while.
Audio, Video, and Conferencing
Plays anything--and I do mean anything. http://www.videolan.org/vlc to download. This is a very simplified video player that handles a vast number of file types and in a pinch can even convert from one type to another.
GNU Image Manipulation Program (GIMP)
GIMP is a freeware PhotoShop wannabe. Since I've never used PhotoShop, I have nothing to compare it to. Still very featureful. http://gimp-win.sourceforge.net/
Now at version 3.0, OpenOffice.org is a completely free suite similar to Microsoft Office. http://www.openoffice.org to download.