My Attempt at Usefulness: Free, Functional Programs (that are at least compatible with Windows, and in no particular order)

Having changed computers and hard drives far too many times, I've compiled a list of programs that I use frequently and that are easy to install. Except for Firefox and OpenOffice, I try to keep things as lightweight as possible. Because my computers violently inhale.

1. Mozilla Firefox

Firefox is memory intensive, but it's manageable, especially considering the features it's got. Chrome may be faster by now, but it had a tendency to crash my computer quite frequently when I tested it in its early stages, and I never gave it another shot.
Firefox has some very shiny add-ons that I don't think Chrome or any other browser has. I use DownloadHelper the most - lets you download pretty much any media file that shows up in a website. Images, videos (from YouTube), music, flash files, whatever.
Also check out Firefox Portable.

2. VLC (VideoLAN) Media Plaver

VLC is a fast, lightweight media player that is magically able to play almost every type of media file ever. This includes the flv files that you download off Pandora and YouTube using DownloadHelper without converting them. It's incredibly easy to "install" (unzip a folder), and easy on my awfully dated computers. Stick it on a flash drive, and you can play any media file ever on anyone else's PC.

3. Pidgin

Pidgin is an IM client that can sign you on to any number of accounts in AIM, MSN, ICQ, IRC, MyspaceIM, Google Talk, and a bunch of other protocols I've never heard of at the same time. Unfortunately it doesn't have one for the abomination that is Facebook Chat, but it's easy to install, it's pretty lightweight, and I'm too lazy to go find/configure a program that does work with fb chat. And behold Pidgin Portable!

4. IrfanView (with the Graphic Viewer Plugins)

IrfanView is a very fast, very lightweight image/media viewing utility. This will probably cover anything that VLC doesn't, can convert file formats, print, and create quick slideshows (which are useful if you happen to arbitrarily need one for a school assembly and you're working tech). Again, works off a flash drive.

5. Alarm

Pretty self explanatory. Alarm clock for your computer that can display a message and play a default sound or an mp3 of your choice. I always wondered why XP didn't come with something that does this. There are some cool online ones, but they obviously require you to be online. Don't think this one can go on a flash drive, but not positive.

6. OpenOffice.Org

Ah, the glorious free M$ office ripoff. If you're poor and/or don't want to shell out 70 bucks for office software, this is your replacement for Word, Excel, Powerpoint (although I am a big fan of Powerpoint), and Access. Also includes a program for drawing. Not as full-featured or fast as their Microsoft counterparts, but they get the job done, for school and your book-writing needs. Yes, it does come portable, but it's big and slow off a flash drive so I would only use it in case of emergency.

7. AbiWord

For simple word processing and Word 97/2000/XP compatibility (note: because it cannot handle many features, certain Word files will not retain their complex formatting), use AbiWord. Fast, doesn't eat up your computer's resources, and can go portable.

8. Sumatra PDF

If you need to read a PDF and don't want to deal with the long load time from Adobe's PDF viewer, this is the program for you. Outline view on side, but no text highlighting. Portable, but I've had trouble printing on some computers.

9. 7-Zip

Free, fast, and very capable file compression/decompression program. Compatible with .zip, .rar, .7z, and others. Portable as well.

10. InfraRecorder

Lightweight CD/DVD burning software. Quick, painless, and portable. Probably the easiest way to burn an iso file there is.

11. Notepad Replacements: Notepad2 and Notepad++

I know there was another similar program, but I can't find it right now. In any case, these are very lightweight (and portable) simple text editors that are not quite as bare as the standard notepad. They have syntax highlighting and some other cool features. Notepad2 for example can become semi-transparent, and Notepad++ has tabbed documents and syntax highlighting for many specific programming and scripting languages.

I could probably go on for a while, but these programs will do the basics of nearly everything you need from your computer. Here's a list of other programs to check out (without hyperlinks
because I'm lazy):

Mozilla Sunbird (calendar)
Eraser (really delete files from your disk)
WinMd5Sum (Md5 comparisons)
Toucan (encryption/synchronization)
Eclipse (IDE for Java, C)
SpeedCrunch (calculator)
Task Coach (to do/task manager)
PDFTK Builder (split, combine, etc. PDFs)
Audacity (Audio editor/recorder)
Blender (3D modeling, animation, etc.)
GIMP (Image editor [poor-man's Photoshop])
Mines-Perfect (Minsweeper clone with many extra modes)
Frets on Fire (Guitar Hero clone)

One Additional Program for the Technologically Inclined - A Hard Disk Diagnostic Utility

GWScan
Download, extract, and burn the .iso file to a CD to create a bootable HD diagnostic tool. Boot off the disk to run GWScan. Allows you to check the disk for errors and attempts to fix them (and often succeeds).