A really good defrag program. Piriform Defraggler

Avira AntiVir Personal - Free Antivirus is a comprehensive, easy to use antivirus program, designed to offer reliable free of charge virus protection to home-users only.

http://www.free-av.com/

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AVG Anti-Virus Free Edition is a free anti-virus protection tool developed by GRISOFT for home use. We invite you to join the millions of satisfied customers worldwide who have downloaded the software and now enjoy the benefits of AVG Anti-Virus Free.

http://free.grisoft.com

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Ad-Aware 2008 Free Protect yourself against identity theft, online fraud, and other cyber crimes with the world's most popular anti-spyware.

http://www.lavasoft.com/products/ad_aware_free.php

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TrendMicro™ HijackThis: A general homepage hijackers detector and remover.

http://www.trendsecure.com/

Don't have money for Adobe PhotoShop?

Paint.NET is image and photo manipulation software designed to be used on computers that run Windows 2000, XP, Vista, or Server 2003. It supports layers, unlimited undo, special effects, and a wide variety of useful and powerful tools.

http://www.getpaint.net/

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Picasa is a software application for organizing and editing digital photos.

http://picasa.google.com/

CCleaner is a freeware system optimization and privacy tool. It removes unused files from your system - allowing Windows to run faster and freeing up valuable hard disk space. It also cleans traces of your online activities such as your Internet history. But the best part is that it's fast (normally taking less than a second to run) and contains NO Spyware or Adware!

http://www.piriform.com/ccleaner

(Cool Website For Software Modding Your Video Cards!!) mvktech.net is a cool website that has everything for video card firmware such as: CoolBits, Detonator, ExperTool, LiteForce, nHancer, NiBiTor, nTimings, NVChk, NVCleaner, NVEmulate, nvFlash, NVTempLogger, NVTray, NVTweak, OmniExtremeEdit, Precision, VGABios, WFFlash, X-BIOS Editor, ATI BIOS Editor, ATI Tray Tools, ATIFlash, ATITool, ATIWinFlash, FlashROM, RaBiT, RadClocker, RadLinker, RBEditor and WinFlash.

http://www.mvktech.net/   -----------------------------------------------------------------------------------------------   7-Zip, free Compression Utility, supports 64bit as well
http://www.7-zip.org/  

Feel free to post any Free Kickass Software you like!!

Please add links and pictures!

Iobit Smart Defrag. Best free degrag toool.
Driver Sweeper, Ceans up all the trace of video drivers before installing new ones
Malwarebytes' Anti-Malware: Malwarebytes. Excellent Anti Spyware too, same thing for asquared free.

http://www.openoffice.org/ OpenOffice is an amazing free open source alternative to MS office - reads and writes .doc .docx .odf .pdf and much more :O 

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http://www.cccp-project.net/ Combined community codec pack allows you to play back basicaly any format in your fav media player 

http://www.iobit.com/advancedwindowscareper.html Advanced systemcare is a free software that cleans up and optimize your computer to make it run fast.

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http://www.iobit.com/gamebooster.html Free software that allows you temporary close the background programs to make your game runs faster.

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http://www.blender.org/ A free open source software that allows you to make and animate 3D model.

Hotspot Shield - A free VPN for Windows, Mac, and iPhone

Hotspot Shield protects your entire web surfing session; securing your connection at both your home Internet network & Public Internet networks (both wired and wireless). Hotspot Shield protects your identity by ensuring that all web transactions (shopping, filling out forms, downloads) are secured through HTTPS. Hotspot Shield also makes you private online making your identity invisible to third party websites and ISP’s.

• Secure surfing on public networks
• Hulu outside the US
• Unfiltered internet at work/school (careful about this!)

TeamViewer5 remote computer control--FREE

http://www.teamviewer.com/index.aspx

Spectro:

• audio file analyzer for windows.
• frequency cutoff indicator 
• reads FLAC, APE, MP3 and WAV files

I think its a helpful tool to find out if ur audio files r transcodes or just bad rips.  FYI people rip from the cds have the cut off frequency above the 20KHz.   

Lossless FLAC file loaded

MP3 (lame v0) encode of the same file

foobar2000

• advanced freeware audio player for the Windows 
• Supported audio formats: MP3, MP4, AAC, CD Audio, WMA, Vorbis, FLAC, WavPack, WAV, AIFF, Musepack, Speex, AU, SND... and more with additional components.
• Gapless playback.
• Full unicode support.
• Easily customizable user interface layout.
• Advanced tagging capabilities.
• Support for ripping Audio CDs as well as transcoding all supported audio formats using the Converter component.
• Full ReplayGain support.
• Customizable keyboard shortcuts.
• Open component architecture allowing third-party developers to extend functionality of the player.

I personally find this player better than winAmp and windows media player for a  music player.  The thing that surprised me the most about this is that the G15 keyboard media buttons on top work with this player unlike winAmp which doesn't.  

http://www.foobar2000.org/

Dont forget amout Microsoft Essentials.

http://www.microsoft.com/security_essentials/

I like FileHippo Update Checker.

Checks for many programs that you have installed and let you know if there are any updates for them and recognizes propert O/S and bit structure...

http://filehippo.com/

To download:
http://filehippo.com/updatechecker/

Some others:
CPU-Z and other programs from CPU-ID.
http://www.cpuid.com/softwares.html

Stability Tests:
Prime95 ---> http://www.mersenne.org/freesoft/
Intel BurnTest ---> http://www.softpedia.com/get/System/Benchmarks/IntelBurnTest.shtml

Malwarebytes it's a really good antimalware program. All you do is run it and it scans your pc for malware and when it is done scanning all you have to do is select remove selected. I use it when I am working on client's computers that have virus' and it works everytime. sometimes i have to use another program called Rkill which kills the virus' process so it can detect the program. Here is the link: http://www.malwarebytes.org/

Here is a screenshot:

Here is the RKill link: http://download.bleepingcomputer.com/grinler/rkill.exe

Here is a screenshot:

for editing a game fiel i woudl recommend NOTEPAD++ it's like notepad. but it has a better interface co you can see at wich line you are. and if ou are programming it is also very useful
DAWNLOAD LINK : http://sourceforge.net/projects/notepad-plus/

We need to add more free kickass software..

How about Google Toolbar, as it automatically ads spelling correction to forums like this. Which some of us need.

http://toolbar.google.com

Ninite : The Easiest, Fastest Way to Update or Install Software. Just pick your apps and click Get Installer. Ninite does the rest — fully automatic.

http://ninite.com/

VLC = best media player I've used.

A couple off the top of my head; KMPlayer and XBMC.

Okay, one that I use A LOT: Ultimate Boot CD.

It is actually a collection of Linux and DOS bootable images in a well organized menu, allowing everything from burn-ins, memory and equipment diagnostics, right down to data and disk backup, recovery, and partitioning. It even has a bootable antivirus utility useful in repairing crashed systems for file recovery.

A few more.

Gimp - GNU Image Manipulator Program. Great Photoshop alternative.

VirtualDub - program used for cutting and encoding video. Nothing fancy though.

Microsoft Visual c++ 2010 Express - Pretty damn nice C++ compiler.

Mozilla Thunderbird - Screw you multiple email accounts with all the different passwords.

Motion-in-Joy - Hook up console controllers to the PC for racing games or emulators.

Truecrypt - Hide all ur pr0nz and other incriminating stuffz with government level encryption.

Handbrake - Quick video encoding for compatibility with most any device.

Offline NT Password and Registry Editor - The key to most any password protected Windows NT based PC.

DVD Shrink - My go-to program for DVD rentals. Hard Drive sold separately.

This is all I can think of currently. Enjoy the random software.

I use Defraggler, CCleaner and there is a program called File Shredder which is free and does an amazing job of getting rid of files.

VLC
7-Zip
Infranview (for viewing extremely weird/rare image files)
Winamp (good alternative to things like iTunes)
Razer Game Booster
Paint.net
uTorrent
Dropbox

VLC, HandBrake, CCleaner and Defraggler are some of the best I've used. HandBrake is probably the best video encoder hands down and I've used a lot over the past 8 years or so.

HandBrake is a life saver. Sometimes the pro video programs create the best video, but only if you let them build HUGE files. Going in after the fact with HandBrake and it's smartness, you can drop that video down to half (or less, sometimes MUCH less) with a follow-up pass.