Operating System Stuff

Slackware Linux
One of the oldest, and in my opinion the best, Linux distro around.

Debian Linux
Very good Linux distro with a huge software repository. I switched to it from Slackware when I built my new 64-bit machine.

OpenBSD
Very secure version of BSD. I use it on my router.

LinuxQuestions.org
A great source of information about Linux and *BSD.

Fluxbox
My favorite X window manager.

Opera
A very good web browser.

Programming Stuff

GCC
The GCC compiler.

Emacs
A flexible, programmable text editor.

MingW
A native Windows port of GCC. The compiler of choice when forced to use Windows.

C++ FAQ
Every language should have a FAQ like this.

SGI's STL documentation

Perl
A very powerful, cross platform scripting language.

Perl Monks
Perl forum and more.

Objective Caml (OCaml)
A fast, portable, strongly typed programming language with type inference. Originally caught my attention for being "faster than C" in some benchmarks.

Erlang
A programming language focused on "shared nothing" concurrency. Originally created by Ericson for use in telecom apps. It looks neat, but I haven't really got the hang of it yet.

Lambda-The-Ultimate
A forum about functional languages and theoretical computer science. A lot of it goes over my head, but it's still a good place to find papers to read.

Koders.com
Code search engine.

Ada World
A bunch of information about the Ada programming language and links to libraries, projects and bindings for the Ada language.

Tiny XML
A small, portable XML parser. It's not as powerful as some larger parsers, but it's fast and usually powerful enough.

Journal of Object Technology
An online journal edited by one of my old professors. Focuses a lot on Java.

Graphics Stuff

Rhino3D
A high quality NURBs modeling/CAD program.

3Delight
A high quality 3D rendering program compatible with the Renderman specification. The first license (for two processors) is free.

SoftImage
A very high quality 3D modeling/rendering program often used for computer graphics in games and movies. Unfortunately, it's very expensive.