Sourceforge's GNU development tutorial - automake, autoconf, libtool, gcc, and all the mysteries thereof explained.
Advice From An Old Programmer - The wisest and most intelligent 580 words you will ever read on the subject of programming. Why not memorize it by heart and recite it every morning like the pledge of allegiance?
Syntax Across Languages - A guide which groups programming language elements by function, across all languages. Any way to say it, no matter what language you're using.
Programming Tutorials Directory - A link directory to programming tutorials for an oddball assortment of languages. Sometimes has dead links.
Byte MyCode - A pastebin of code snippets, which users can vote up or down like on Digg.com.
The Semicolon Wars - Did you ever consider that the number of programming languages rivals the number of human spoken languages? And that spoken language had millennia to evolve and diversify, while programming languages have all appeared in a half-century?
Lambda the Ultimate - The programming Languages Weblog.
How I Learned to Program - A very clear path laid out by a person great at explaining things. Follow this example.
Brendan Gregg's Specials - A certified mad scientist of the command line comes up with some hilarious, satirical command-line tools. Advanced humor for sysadmins. Implement fuzzy logic with "maybe", have the undead haunt your system with "mkzombie", and find out the star sign of your running processes with "lsss".
programming in the twenty-first century - Not particularly an open-source blog, but a great blog by a deep-thought author examining the world of code. Startling insights from a keen observer.
Resources For Web Design - A huge blinkin' directory with every web programming resource imaginable. Surprisingly well-maintained.
Think Vitamin - In a sea of web developer blogs, one wave reflects the sun twice as brightly.
Ajaxian - Someday there will be another AJAX blog to point to...
Most Wanted Ajax Techniques - Over fifty tutorials and examples for the most in-demand AJAX methods.
AWK one liners - One-liners in awk.
awk at Everything2 - A surviving scrap of awk culture.
Famous Awk One-Liners Explained - An in-depth blow-by-blow account of what all those funny characters do. Check at the bottom for links to the rest of the series.
Shell-Fu - Shell script snippets
SHELLdorado - Probably the most famous shell scripting resource on the web - maybe it's because of the cool name.
Advanced Bash-Scripting Guide - The Bash Grimoire! You can read it for ten years, and still learn something new every day.
Bashish - The classic Bash prompt customizing package. +20 geek points.
BASH Cures Cancer - An enthusiastic Bash blog.
Bash One-liners - A handy blog of Bash one-liner commands, with explanations and examples.
Programming in C - You might as well start here.
C Puzzles - Sharpen your C-programming wits with these code snippet puzzles.
Kernel Glossary - Since the Linux kernel is written in C, knowing it becomes instrumental to knowing C.
Jack Crenshaw's "Let's Build a Compiler" - While it applies to a lot more than just C, it's the kind of thing that occupies the minds of C programmer's minds. Worth a read just to understand a little bit of it, even if you don't actually build your own compiler.
The International Obfuscated C Code Contest - As of 2011 - it's BACK! LOL, OMG, WTF, BBQ, sqeeeee!
W3 CSS Tutorial - Might as well start here.
CSS tests at hixie.ch - This site hosts a wealth of web code examples. Since getting floating boxes to behave is one of the biggest aggravations of CSS, this test suite is especially instructive.
Stu Nicholls' CSSplay - An amazing mad scientist pushes CSS to places it was never intended to go. The Mr. Wizard of CSS. Explore the demos, find all the surprises.
W3 HTML Starter - Why do we need this? Aren't all babies born talking in HTML tags? I was. What's wrong with everybody else?
HTML Playground - Live-test tag creation. Much, much less fun than it sounds.
Anthony Thyssen's Image Magick Examples - Quite possibly the best online manual ever written for any application; definitely the best for Image Magick. This treasure explores everything you can do with Image Magick, which is about 100x what people expect to be done.
The Fx Special Effects Image Operator - From the official documentation. The -fx operator is an especially mysterious and little-known tool in Image Magick.
Fred's ImageMagick Scripts - A growing collection of Image Magick incantations.
GNU Emacs Lisp Reference Manual - Good God, has anyone ever read the whole, entire thing?
Lisp Quickstart - Tidy little CLisp guide.
Successful Lisp - What is it about Lisp that makes people love to write huge books about it?
The Common Lisp Cookbook - Recipes for Lispers.
Programming in Emacs Lisp - Emacs and Lisp go together like a wink and a smile.
PHP Manual - The astoundingly complete guide to one of the biggest, ugliest, and most-essential languages ever.
10 Tips That Every PHP Newbie Should Know - For that matter, salty veterans should know them too.
PHP MySQL Connect to a Database - the most common thing you need PHP for anyway.
15 Cool Things About PHP That Most People Overlook - Not so sure about the "cool" part. For instance, the "==" vs "===" thing is more something I'd call "a reason to find whoever thought of that and beat them like they stole something," but anyway, these are informative.
Python Documentation - Delicious, yummy Python, might it always reign supreme!
IBM's Python 101 Cheatsheet - Thank you, IBM!
Dive Into Python - The book that made Mark Pilgrim famouser.
Python and Pygame Examples - Outrageously easy-to-follow examples of basic video game concepts done for Pygame.
Seder's Grabbag Tutorials - Sed tricks, both stupid and smart.
Regular Expressions - Jamie Zawinski hates them, we still can't do without them, they are married to sed. Find out why.
SQL Manual - Ugh! The world's most boring topic, ever.
SQL Zoo - No, putting it in a zoo still doesn't make it exciting.
MySQL Tutorial - I pity anyone who needs this, including me.
Tclers Wiki - Yes, it has one!
Tcl/Tk Cookbook - Almost a guilty pleasure.
Tutorial for Cool Languages - Worth pointing out because it has a great GUI-building tutorial.