DXF

AutoCAD DXF Reference
Official echnical information about DXF from its creators Autodesk.
http://usa.autodesk.com/adsk/servlet/item?siteID=123112&id=8446698

DWG DXF Convert
An AutoCAD DWG/DXF bi-directional translator built using the powerful DWGDXFLib library. It converts an AutoCAD DWG file into an AutoCAD DXF file and vice-versa without the need of AutoCAD. DWG DXF Convert also supports batch conversions of multiple DWG or DXF files.
http://www.sycode.com/products/dwg_dxf_converter/

DXF to OpenGL
This program reads a 3D graphics image file, in the DXF data format, and displays it using OpenGL.
http://www.bearcave.com/dxf/dxfintro.htm

DXF2rad
A converter to translate 3D DXF data to the Radiance scene file format, available for multiple platforms.
http://www.schorsch.com/download/dxf2rad/