Sup dudes. I've been known to participate in a few computer discussions, and am currently working at a comp shop here locally ( Onyx Systems ), and I've learned a few things about computers in my time working with them. Over the course of my time working on computers, I've run across a lot of interesting tips, tricks, hacks, and useful pieces of software. I'm going to list a few of them here, in no particular order.
The list:

http://www.openoffice.org
Open Office is the free alternative to Microsoft Office. It's still in active development and provides all the programs that MSOffice does.

http://www.free.grisoft.org
Ah, AVG. How I love thee. Okay, shitty rhymes aside, AVG is a bad ass piece of software. It hunts down, tracks, chases after, beats down, and brutally rapes any virii in your system. It's my antivirus of choice.

http://www.ccleaner.com/
CCleaner is a beautiful piece of software. All that ♥♥♥♥ IE/Firefox/etc piles up? CCleaner kills it. I clean mine once a month, removing anywhere from 500mb to a gig of files each clean. Always back up your registry if you're cleaning your registry at any time except immediately following a clean install.

http://www.blender.org
Blender is beautiful. Free 3D modeling software with built-in physics engine with soft-bodies, rigid-bodies, and water. It's open source and expandable too!

http://www.yafray.org
Yet another free ray-tracer is a ray-tracing engine that allows for photorealistic quality. I use it in Blender as a plugin.

http://www.ventrilo.com
Ventrilo, also known as Vent, is a free VOIP(Voice over IP) program that allows you to speak to people across the internet, provided you have a mic.

http://www.rarlabs.com
WinRAR is a universal unpackaging tool. What can I say, it decompresses compressed things.

http://www.7-zip.org
7zip is the same thing as WinRAR. Some claim it's better, some claim it's worse, I don't care I use WinRAR because it's installed.

http://www.fraps.com
A nice little video capturing program. Used primarily for games. The free version has a watermark though.

http://www.hyperionics.com/hc/
Hypercam is a lot like fraps, but you get to choose what area of the screen to capture.

http://www.mirc.com
My IRC client of choice. Sexy, allows scripting, and well.

http://www.videolan.org
VLC is a nice media player that I use for playing videos, considering it plays anything.

http://www.winamp.com
Winamp is a nice little media player that I use for my audio files.

http://www.gimp.org/
Gimp is a replacement for photoshop. It's licensed under GNU.

http://audacity.sourceforge.net/
Audacity is a rad audio editor, and it's free too!

http://www.truecrypt.org/
TrueCrypt is an awesome encryption software. I really can't convey how cool it is, go check it out.

http://www.alcohol-soft.com/
Alcohol is an imaging program for burning CDs, ripping them, and mounting images to virtual disks through iso files.

http://www.futuremark.com/
Futuremark is a benchmarking program to test your computer.

http://www.passmark.com/products/bit.htm
Like futuremark but less rape. We use it down at the shop as a break-in for the computer on new builds. Tests your computer, makes sure everything's running properly, etc etc.

http://www.mozilla.com/firefox/
Firefox is my browser of choice. Open source, bare bones, completely extendable. What's not to love?

http://www.opera.com/
Opera is another free open source browser. I used it for a while but felt it was too cluttered and bloated with unnecessary options for my liking. It goes here nevertheless for a lot of people like it.

http://www.apple.com/safari/
Safari is another web browser, just recently ported from Mac to Windows. When I say recently I mean months but whatever. Have yet to use it, so no comment, but it goes here for variety.

http://www.portalgraphics.net/en/
OpenCanvas is a sexy little drawing program that provides a lot of useful tools. Our local furfag and arr-teest Jack uses it. It also happens to have online connectability for epic multiplayer paint.

http://www.almico.com/speedfan.php
SpeedFan allows you to set how fast the fans in your computer go. Very useful if your computer is OC'd or is in a poorly ventilated area.

That's all I have for now. Feel free to add on to the list.

http://www.pidgin.im/
Free, open-source, multi-protocol IM client. Have a shit-ton of instant message accounts spread across the different protocols (AIM, Yahoo!, GoogleTalk, ICQ, MSN, and many more)? Pidgin lets you access them all at one from one piece of software.