Here is a list of free downloads to make your Windows system more functional:
File types listed in orange, protocols in yellow.
Prices and demo conditions listed in green.
Network:
Communication:
Browsers:
Diagnostics:
Other:
  • VNC - view windows over the network in Windows/Mac/Linux
  • SmartFTP - FTP client
  • WinSCP - SCP client
    eMule, Limewire, SoulSeek, Peercast, DC++, Furthernet, Shareaza

File Types:
WinRar - RAR/ZIP file compressor
Adobe Acrobat - PDF file reader
Ghostview - PS file viewer

Music:
WinAmp, Zinf - MP3 Player
Exact Audio Grabber - MP3 Ripper
Easy CD-DA Extractor - MP3 Ripper
CloneCD - CD Copier

Unix on Windows:
Cygwin - UNIX emulation for Windows
Putty - SSH client
Emacs - text editor


Editors:
Gimp - image manipulation
UltraEdit - text editor
Amaya - HTML editor
WinHex - hex editor
010 Editor - Professional Hex Editor with histogram function!
Programmer's Notepad - source code editor


3D Modeling:
MilkShape3D - $25/30 days - 3D modeler
Ultimate Unwrap3D - $50/no save - 3D texturing tool
Maya PLE - 3D modeler free trial edition


Games:
Nester- NES emulator


Utilities:
FolderSizes - $50/15 days - disk space visualization


Other lists:
Dave's List
OSNews - Apps you can't live without
Slashdot - first 10 apps on a new install