Free Tools

Here are a number of free tools that I have found to be very useful.

Backups

Mozy Easy automatic online backups with 2GB of free storage (a little more space for both you and me if you sign up using referral code K292GA).
Directory Compare This handy utility will compare and/or synchronize folders including network shares and can be used for simple backups. Visit the author's home page for more handy tools: http://tp.lc.ehu.es/jma.html

GIMP GIMP is a versatile graphics manipulation package.
Hugin Panorama photo stitcher.
jhead Exif Jpeg header manipulation tool (can use -autorot flag in conjunction with jpegtran to automatically rotate images based on orientation data stored by cameras that support including many Canon Powershots).
jpegtran Lossless jpeg manipulation including rotation (direct link for .exe version is here).
ImageMagick I mainly use this for batch picture resizing (mogrify -resize *.JPG 1600x1600)
gPhotoShow Photo screen saver with support for multiple monitors
Slideshow Slideshow application with support for multiple monitors (not a screen saver, but useful for cycling through images on an extra display for example)

Firefox Web browser (favorite add-ons include Copy Plain Text, Auto Copy, ShowIP and SwitchProxy Tool)
Skype Encrypted text & video chat that just works (even through firewalls)
PuTTY Free telnet/ssh/serial client which supports tunneling and much more.
FileZilla FTP client which also supports SFTP
UltraVNC Remote control software
IPerf Command line bandwidth test tool (a graphical front end is also available called JPerf although I haven't used it much).

KeePass Password Safe Secure, encrypted password storage with cross platform support including blackberry and other mobile devices.
TrueCrypt Free open-source disk encryption software for Windows 7/Vista/XP, Mac OS X, and Linux (I use it mostly for a virtual encrypted disk within a file which is mounted as a real disk).

MPEG Streamclip Simple video editor that can read multiple formats and export them to QuickTime, DV, AVI/DivX and MPEG-4.
VLC media player The cross-platform open-source multimedia framework, player and server
VirtualDub Video capture/processing utility mainly geared towards AVI

1-4a-rename A file renamer which renames many files at once (handy for combining pictures from multiple sources and prepending numbers to keep them in order).