Useful Freeware Apps

[Bargo]

Here's some for inclusion that I use, I'll post more as they come to mind:

For starters:
PortableApps is a good resource for applications of all kinds that you can install and run from a USB disk, ie. you don't have to go through the painfull windows install process and have it dump files everywhere.

Now onto categorized stuff..

Internet
Mozilla Sunbird - for those that want Outlook Calendar features but don't want outlook.
Pidgin - instant messenger that works across many different providers, ie. aol, MSN, yahoo.
Trillian - same as above.

Audio
Mp3tag - very useful program for batch tagging of mp3s. Also FAST, unlike itunes and the like.
Audacity - audio editing and conversion.

Video
SUPER Video Converter - converts between a huge number of formats. Very useful to convert movies into a format suitable for playback on ipods.
Handbrake - DVD to MPEG4 converter.

Utilities
AdAware and Spybot S&D both do spyware detection.
AVG Free Edition - regularly-updated virus scanner.
Dosbox - a DOS emulator, so you can play all your old DOS games and apps.

[Skie]

Zone Alarm - Firewall