Pixlr
http://www.pixlr.com/editor/
Pixlr is a free web based image editor. It has some cool functions to be something that requires no download or installation.
Open Office
http://www.openoffice.org/
I refuse to put M$ Office on any of my machines and this is an awesome alternative.
Celtx
http://celtx.com/
This is a free script writing app. Its great for screenplays, comic books, or anything you need a formatted outline for.
SketchUp
http://sketchup.google.com/
Google's SketchUp is kind of a CAD package and kind of a 3D modeling package. This in combination with Google's huge 3D object library makes this a great resource.
Skype
http://www.skype.com
Phone, web conference, screen sharing, fax, etc, etc.....
KMplayer
http://kmplayer.en.softonic.com/
I hate Windows Media Player. This is a good alternative....
Picasa
http://picasa.google.com/
A photo viewer and media manager. I use this in place of windows picture viewer so I can scroll through pics with my mouse wheel.
Thunderbird
http://www.mozillamessaging.com/en-US/thunderbird/
My email app of choice. Tabbed emails rock.
7Zip
http://www.7-zip.org/
Compression utility that works on just about everything...zip, rar, tar, iso, etc...
FontFrenzy
http://www.sdsoftware.org/default.asp?id=5936
Removes and stores all fonts except those that were present when Windows was first installed.
GXTS Screensaver
http://goheer.com/products/GxTS/
Displays how long it has been running along with other vital system information (network traffic, discs, mem, etc). Very low CPU load 0% -4%
Teamviewer
http://www.teamviewer.com
The easiest remote desktop solution I have found. You dont even have to install it.
CDburnerXP
http://cdburnerxp.se/
CD/DVD burning software.
Trillian Astra
http://www.trillian.im/
Instant messaging...includes aim, yahoo, msn, facebook, irc, etc......
Reaper
http://www.reaper.fm
A digital audio workstation: a complete multitrack audio and MIDI recording, editing, processing, mixing, and mastering environment.