Free sh-it edition

Some of my favorite and commonly used software that

A) Works
B) Is free

There are plenty more... and some will follow.

System Utilities

Anti-virus (free edition)
http://www.avast.com/

Disk Defrag

http://www.auslogics.com/en/software/disk-defrag

CD/DVD Burning
http://infrarecorder.org/

Zip/Archive Utility
http://www.7-zip.org/

Entertainment

Media Player
http://www.videolan.org/vlc/

Graphics
I am torn between

Paint.net
http://www.getpaint.net/

and

GIMP
http://www.gimp.org/

Virtualization
VirtualBox
http://www.virtualbox.org/