[inkista]

Few of mine, most are non-photography, and there's a decided bias towards GNU and things found on sourceforge...

• Google Chrome (fast replacing Firefox for me).
• ClamWin (free antivirus). ClamAV-based app. (Sidenote: Spyware Blaster and/or AdAware are also good things to have on a Windows box.)
• VLC. The swiss army knife of all video players. Plays Matroska just fine as well as all your usual suspects, not to mention turning your dvd-drive-equipped computer into a region-free PAL/NTSC-converting dvd player.
• TrueCrypt--encryption software. The only solution I found for keeping my stuff encrypted on a USB stick and still use the files on Linux, Windows, and OSX. And hey, who doesn't want to use the same encryption as the NSA?
• Hugin. Damn fine pano stitcher.
• Mathmap. One of the few GIMP plugins that has no peer on the Photoshop side.
• XAMPP Portable. I like carrying a working Apache/MySQL/php installation with me on a USB stick. Being able to turn any box into a development webserver with all the bells and whistles, yet leave no tracks behind, is a good thing.
• OpenOffice. Sun does good things. OOO is finally getting mature enough to be not just a free office suite, but a good office suite.
• Eclipse. Ok, it's funky and the plugin mares' nest can be hideous, but it's still one cool IDE that everybody's tweaked for themselves so you can use it for developing in everything: C++, C, Java, Perl, Python, Ruby, Ada, shell scripts, (not to mention accompanying makefiles and SVN/CVS integration) hell, I wouldn't be surprised if you could do Basic and Fortran in the sucker. And it's not just for programming: HTML, XHTML, XML, XSLT, **********, PHP... Eclipse is endlessly useful. And it's a heckuva lot easier to use for developing XSL transforms than plain ol' Xalan.
• Subversion. What? You think version control is just for open source programmers? Remember that the next time you're writing the great American novel, and you think you want that one paragraph back that you had in the passage you deleted two weeks ago...

Let's hear it for open source.