Download Squad

Media: Songbird, VLC, Handbrake, DVD Flick
I've been using VLC for ages, and it does everything I need as my video player of choice. Audio duties I leave up to Songbird, which has matured into a fantastic application over the past two years. I use Handbrake to, uh, rip my non-encrypted, personal DVDs. DVD Flick lets me burn said rips back onto a disc.

File Transfer: Free Download Manager, Cabos, eMule
FDM is a very underrated torrent app, and it has plenty of other download-boosting abilities as well. I chose it over Vuze because I need FDM's extras (partial zips, Flash downloading, Rapidshare integration) more than Vuze's additional media-handling chops. Cabos trims Limewire down to the bare minimum for the occasional one-off Gnutella download. As for eMule, I use it to find things that I can't find elsewhere.

Imaging: ZScreen, Inkscape, Gimphoto/GimPad, Flickr Uploadr
If you're comfortable with Photoshop but looking for a free alternative, go with Gimphoto instead of Gimp – the interface is very Adobe-esque. For vector image jobs, Inkscape can't be beat. ZScreen handles my screen captures and Flickr Uploadr, well, it does what it says.

Burning and Backup: Infrarecorder, WinCDEmu, Bonkey, and DirSyncPro
These three apps make short work of mounting disc image files, burning just about anything, syncing folders, and keeping a current copy of your files in a safe location.

Messaging and Social Networking: Pidgin and Spaz
Don't sic Mr. Stallman on me – I know Spaz is built on Adobe Air, but the client itself is open. As for multi-protocol messaging apps, Pidgin is a tough bird to beat.

Maintenance and Utilities: 7zip, Belvedere, Ultra Defrag, Disk Cleaner, TrueCrypt
Lifehacker's Belvedere is a great way to organize your files and folders with minimal effort. Ultra Defrag and Disk Cleaner (and a handful of helpful plugins) keep your hard drive clutter free and performing its best. 7zip waits in your context menu to extract files from (or cram files into) archives of all kinds. For encrypting files, folders, or entire volumes, Truecrypt is fast and reliable.

Desktop Enhancements: RocketDock, Launchy, Virtual Dimension
You don't really need both RocketDock and Launchy. If you prefer eye candy, go with Rocket Dock. If you're a keyboard magician, go with Launchy. I run Virtual Dimension because my forays into Linux have me hooked on the benefits of virtual desktops.

Games: AssaultCube, Enigma, FreeCiv, LexJongg, LinCity, Neverball, Nexuiz, PokerTH, TORCS, Tremulous, WinSudoku, Wormux, Zombies.
Using your computer shouldn't be all work, all the time. Kick back and relax or give you brain a casual workout with these great games. LexJongg puts a slightly technogeek spin on traditional mahjong. FPS fans should check out AssaultCube, Nexuiz, and Tremulous. FreeCiv and LinCity offer OSS takes on two classic PC simulations. TORCS is a solid 3d racing sim which will hopefully soon include online action. Wormux and Zombies are fun turn-based strategy games. WinSudoku and PokerTH - I'll assume you know what those are all about.

There you go - plenty of great OSS to load on your own freshly reinstalled system (or a friend's)! If I missed one of your favorite apps or games, share it in the comments!