Knowledge for free, in no particular order.

"Information overload"

No excuse to miss:

Articles by Paul Graham
Great essays, a must read.
Joel on Software
Joel Spolsky, one of the most important persons in the field today. For me. Especially read his older, classic posts (or, while you're at it, get his books).
Mark Russinovich
Author of "Windows Internals" and founder of Sysinternals (aquired by Microsoft in 2007).
Coding Horror
Mixed blog on software engineering. Together with Joel Spolsky, he founded StackOverflow, a new platform to discuss development.
IBM DeveloperWorks
A whole magnitude of consolidated knowledge.
Martin Fowler Bliki
"An author, speaker, consultant and general loud-mouth on software development". One of the authors of "Refactoring: Improving the Design of Existing Code", "UML Destilled" and the Manifesto for Agile Development.

Additional material for your daily dose of information overload:

Artima Developer
A "Community of Software Thinkers"
The Daily WTF
"Curious Perversions in Information Technology"
The Old New Thing
Raymond Chen, a senior Microsoft engineer, blogs about "technical nitty-gritty, with a Microsoft focus".
YCombinator News
A collection of blog article links related to software development, with a focus on startups and economics (YCombinator is a venture capitalist); similar to Joel Reddit. Actually, I like the contents of Joel Reddit more.
Sourcefrog
Martin Pool's blogs about... well, I'm not sure.
Scott Hanselman's Computerzen
... wouldn't be listed here if it wasn't for his Babysmash series
The Caffeinated Coder