Here is the list of the software I use on my personnal computer. All of them are free for personnal use :
Malware Protection
AVG Free Edition – Antivirus
Adaware – Spyware removal tool
Spybot – Spyware removal tool
Web
Firefox – Web browser
GTalk – Instant messaging
MSN Messenger – Instant Messaging
ICQ – Instant Messaging
PuTTY – Multi-protocole remote terminal
Productivity
OpenOffice – Office suite
PDF Creator – Creating PDF
Sunbird – Calendar
System
DIRMS Defrag Tools
PowerToys – Tweak UI
SysInternals – AutoRuns : displays what runs at startup
SysInternals – PageDefrag : defrag your pagefile at boot
SysInternals – ProcessExplorer : Task Manager on steroids
Misc
Java
7-Zip – Good free archiver (many archive types supported)
AutoHotKey – Macros for windows
Media
VLC – Media player
foobar2000 – Music player