OS: Debian/Ubuntu Dapper GNU/Linux. Trust me. Ubuntu is Debian. Really. If it ever becomes otherwise, I'll let you know.
IMAP client: Thunderbird
Cryptography client: Enigmail and Thunderbird's internal S/MIME implementation
IM client: GAIM
HTTP Browser: Firefox
Blog software: evan's LogJam for my LiveJournal service, Wordpress for my personal blog service
Audio manipulation: audacity
Raster image manipulation: The gimp
Web development platform: LAMP
Karma handles my LAN's IP masquerading. Karma runs an amalgam of sarge and etch.
Moonunit is my IMAP server and currently hosts the wiki. Moonunit runs an amalgam of sarge and etch.
Avenger handles the blog traffic. Avenger runs sarge.
Norseth is my primary workhorse. My employer owns this computer and provides its use for getting things done (tm). Norseth runs Dapper with CVS/SVN versions of applications I need to tweak.
Steely is my os x box. I haven't touched it much recently because we're considering selling it in order to liquefy some of our assets. So we can watch them drip through our fingers more easily. Gar.
If you haven't read my sysadmin advice, you might do so. It lists a few of the things I do to save time / energy.
I try to use GNU tools whenever possible. I feel that if I am going to be tied down to some particular platform, I want it to be one that I have the source code to. I respect the decision of Microsoft, Sun, Adobe, etc. software users. I understand that having something that does what you need it to *now* is important in many cases. And when the same is true of me, I I do use these proprietary tools. But I prefer to avoid them when possible and support instead the community.