Windows:
KCeasy - OpenFT Filesharing which uses HTTP to transfer files, cool concept for getting around packet shapers.
Netbeans - Free Java Integrated Development Environment
Visual Studio.NET - Free as a part of MSDN Academic Alliance
iTunes - I can listen to about 10 different people's music because of iTunes' capability to share music libraries
Synergy - Allows me to use my regular keyboard and mouse on my laptop through the network.
DVD Shrink - For ripping/burning DVDs
Spy Sweeper - Seems to pick up stuff that Adaware and Spybot S&D miss.
Daemon Tools - Allows you to mount .iso's etc. to a virtual drive
Linux: Most of these have windows versions too, I just don't have them installed in windows.
Net Hack - A fun little roguelike game.
KDevelop - Basically Visual Studio for making linux applications.
IRSSI - Very small text based IRC client, fairly easy to use.
****
Blender**** -
Everyone must try this. It is a free
professional quality 3d modelling/animation program. Which brings us to...
The Gimp - Free photoshop equivalent, goes nicely with Blender.
Super Tux - Who turned mario into a penguin?
Freecraft - Warcraft 2 knockoff, got a Cease and Desist letter from Blizzard. Still available in
Debian's Apt Repository
Open Office - You don't need Microsoft Word, Powerpoint, Excel or any of those if you get this. Compatible with all microsoft file formats.