http://www.techsupportalert.com/ is excellent for finding the best software to do a particular job; it has listings and recommendation for dozens of categories.
Other sites worth searching include
http://nonags.com
http://download.com
tucows.com
Sourceforge (http://sourceforge.net ) is normally used by open source developers to host their apps, so it contains a lot of very useful software for both everyday and highly obscure tasks.
Portableapps (portableapps.com ) is a suite of free software that has been modified to work straight from a USB key or similar.
Lifehacker (lifehacker.com ) often mentions useful software.
Now, some of my favourite free software:
Inkscape http://inkscape.org
OpenOffice http://openoffice.org
GIMP (image editor) http://gimp.org
Ubuntu (operating system) ubuntu.com
Scribus (desktop publishing) www.scribus.net
VLC player http://videolan.org
LyX (typesetting) lyx.org
iTunes apple.com/itunes
Picasa (photo management) http://picasa.google.com
Blender blender.org
Notepad++ notepad-plus.sourceforge.net
Last.fm http://last.fm
You get the idea; there is tons available for free.
There are also quite a few games available: look for enemy territory, cube, cube 2, wormux, tremulous, wolfenstein (a multiplayer game was released for free a few years ago, and it has also been modded to create several more games), Battle for Wesnoth, Area-51 and The Suffering.
I apologise for some addresses not actually being links; Y! Answers only allows 10 per answer.