Free Software

Linux

Ubuntu - The best flavour of Linux for beginners
Fedora - The most open & free version of Linux
Gentoo - For experienced / hardcore Linux users

Browsers

Mozilla Firefox - The best most configurable web browser
Google Chrome - The newest and slickest web browser
Opera - Yet another alternative web browser

Photo / Art

GIMP - An excellent Open Source alternative to Photoshop
Paint.Net - Like Paint but supercharged
Inkscape - Open Source vector graphics editor

Messaging

Skype - Instant messenger, video chat and internet phone application
Live Messenger - Microsoft's instant messaging and web chat solution

Miscellaneous

iTunes - The rocking music library and store, must have for iPods
Picasa - A picture library for your thousands of photos, basic editing too
Google Earth - Map the earth, the heavens and the depths of the oceans
Open office VLC Media Player Audacity WinAmp K-Lite Codec uTorrent LogMeIn TightVNC CDburnerXP ImgBurn 7Zip FileZilla FreeCIV