AVG free Antivirus
Windows Live Messenger
SMPlayer It's better than VLC media player and Media Player Classic. It's able to play the most known video & audio formats without the need of external codecs.
OpenOffice free office suite
GIMP GNU image manipulation program ( Like Adobe Photoshop, but Free )
Foobar2000 Great Free Media Player ( I like this better than Winamp, Itunes, and Windows Media Player )
Opera ( Probably the best Web Browser )
Firefox ( Another great Web Browser )
smartftp, the free secure FTP client for Windows
CCleaner CCleaner is a freeware system optimization and privacy tool.
Linux Operating System ( Ready to dump windows? )
30 Essential Pieces Of Free (and Open) Software for Windows
If that's not enough to get you started go to The Free Software Foundation ( Tons of Great Stuff Here )