Software Development
General
MSDN Microsoft Developer Network
CodeGuru A very good reference site for many languages
The Code Project An excellent reference site for many languages
Programmer's Heaven Another good reference site for many languages
Games
GameDev.Net Excellent resource for game developers
Game Tutorials Good resource for code samples for game coders
HTML & DHTML
HTML Coding Tutorial Probably the best all around HTML reference site
HTML Color Codes A good general HTML color code reference table
DHTML Guru A good website to do some amazing things with DHTML
Dynamic Drive A good resource for ready to go DHTML scripts and code
XML & XSLT
XML Reference O'Reilly's technical introduction to XML
XSLT Reference O'Reilly's technical introduction to XSLT
JAVA & JSP
Java.Sun.Com The official source for the latest Java packages
JavaServer Pages Sun's official site for JSPs
JavaServer Pages examples Some samples on JSPs from the Weblogic site
Core Servlets and JavaServer Pages One of the best books and websites out there for JAVA examples
JavaScript
JavaScript Central Netscape's DevEdge website for the JavaScript language
IRT.Org JavaScript One of the best all around Javascript sites
Perl
Perl.Org The official source for all the latest Perl information
OpenGL
OpenGL.Org The official OpenGL website
NeHe Productions Great site for OpenGL code samples and tuorials
Games Sample Code (Mac) Apple's code samples for the Macintosh
DirectX
DirectX Home Page Microsoft's official DirectX website
NeXe DirectX samples and tutorials
C/C++
C/C++ Resource O'Reilly's extensive website for C/C++ programmers
C#
Visual C# Home Page Microsoft's website for their fully implemented JAVA-like language
Cg
C for Graphics nVidia's site for this new multi-platform high level language
CgShaders Good site for Cg information, samples, and tools