DXF/AutoCad links

DXF is a file format for exchanging CAD files defined by AutoCad.

www.autodesk.com/techpubs/autocad/acad2000/dxf contains the 2000 version of the dxf spec.
A java DXF viewer by Rammi. Recently he released new improved version. Rammi played a big part in getting CadLib to where it is now (a big thank you!). He and I are cooperating on/competing with our dxf viewers.
www.cadtutor.net has some very decent AutoCAD Tutorials.

.NET links

.NET is the new application platform created by Microsoft, and is similar to the java platform.

Microsoft's page with links to useful programming tools.
The Code Project contains lots of useful .NET articles and samples (including one of mine).
Sharp3D is a free vector and matrix math library by Eran kampf is currently used (discontinued, .NET 1.1).
At .NET 247 you can post your .NET questions. Also a good Q&A archive.
The GDI+ faq by a Microsoft MVP.
pinvoke.net is a useful wiki with .NET p-invoke signatures.
Visual Studio Express is the free .NET 2.0 ide by Microsoft.
SharpDevelop is a free .NET ide. It's not bug free and not as smooth as Visual Studio .NET, but it is good enough for most tasks.
CLR Profiler (v2.0) is quite a nice free memory profiler by Microsoft.
NProf is a free performance profiler.
.NET Reflector is a nice tool for inspecting assembly contents.
GhostDoc for generating xml comments in visual studio (not the express editions).
MSDN .NET forums

Wolfram MathWorld, "the web's most extensive mathematics resource".
GameDev.net has lots of articles and resources involving game development, 3D, audio.
The Matrix and Quaternions FAQ is a nice comprehensive FAQ for most common 3D math.

Aptana is a robust, JavaScript-focused IDE for building dynamic web applications (free).
Inkscape is a very good and open source vector graphics drawing application. Drawings are saved in the public W3C defined svg format.
Process Explorer is a very nice replacement of Windows Task Manager. It also shows .NET memory usage and details about garbage collection.
Always forgot those regular expression syntactical details? Try Expresso, a free tool for constructing and testing regular expressions.