Now that I'm home, I can add more, all the ones I use, in fact:

WinRAR: My archiving software of choice.
Dropbox: Automatic backup in the cloud. Use my Referral link, we'll both get more space!
Google Talk: Takes GMail's chat feature out of the chat window.
Skype: For phoning home for free!
FlashGet: Download manager.
Inkskape: Vector graphics drawing program, useful for the odd diagram or doodle.
AShampoo: My preferred burning software.
PowerISO: For easy use of image files.
LastFM: Keeps track of my listening habits.
VLC: Least hassles with codecs ever.
Winamp: I still haven't found a simple replacement that just works.
Calibre: Library app to keep track of the gf's billions of ebooks.
Sumatra: PDF reader to replace Adobe's reader.
ESET Smart Security: The only av & firewall I trust.
Peerblock: Keeps out unscrupulous IP's.