Morpholio Trace - Morpholio Trace is widely called to be the dream software of the designers and architect.
Autodesk DWG TrueView - Get a free DWG viewer to view, open, edit, and convert .dwg files, the native file format for AutoCAD files. DWG Trueview includes DWG TrueConvert.
Free DWG Viewer - Free Viewer for DWG, DXF, DWF View AutoCAD DWG/DWF/DXF files View & measure DWG, DXF, DWF
Autodesk Design Review - Design Review lets you view, mark up, print, and track changes to 2D and 3D files.
Teigha File Converter - For converting between different versions of .dwg and .dxf
ZWCAD Viewer - Cross-Platform .DWG | .DXF | .DWT R12-2013 Viewer