Source Control and Bug track:
http://www.mantisbt.org/ , Mantis: Open source bug tracking system for multiple projects. It is free!
http://subversion.tigris.org/ , Subversion: Open source code repository and code control. Multiplatform and feature rich.
Windows Administration:
http://www.SysInternals.com, Microsoft acquired Sysinternals in July, 2006. Whether you’re an IT Pro or a developer, you’ll find Sysinternals utilities to help you manage, troubleshoot and diagnose your Windows systems and applications.
Web Development:
FireBug, Excellent addon tool for Fire Fox. You should have this.
NotePad++ Very good geneal purpose text editor.
WAMP Apache, MySQL, PHP on Windows. Single install with utilities if you don't want to mess with configs.
Desktop Apps:
7-Zip, file compresison, multiple formats, open source.
FileZilla, my FTP
KLite Codec Pack, codecs.
Portable Apps, you can carry your favorite portable programs in a USB drive. Use any USB flash drive, portable hard drive, iPod/MP3 player, etc
Interesting:
http://eyeos.org/ open source web OS. There are others out there, but this is Open Source and apears stable.
Content Management Systems:
CMS Made Simple: It is really simple and powerful. You can add code snippets inside layouts and it is evaluated in run time. It has admin menu to change layouts and styles. you can also edit them. You can install different Modules or develop your own module. It has good level of supporting documentation.