What viewer can be used to display/view .DWG files?
To view DWG files up to version 2002 you can use the free Autodesk viewer Volo View Express. It supports DWG, DXF and DWF files, Object Enablers (for viewing Desktop drawings and other custom entities) and can be also embedded into other applications as an ActiveX object.
For DWG versions 2004, 2005, 2006, 2007 and higher you can use newer Autodesk applications - the free Autodesk DWG TrueView (supports also object enablers), "Autodesk DWG Viewer" or "Powered by Volo View".
Autodesk Design Review (former "Autodesk DWF Composer", replacing older 'Volo View') supports (besides viewing, measuring and printing) also electronic redlining of DWG and DXF files with publishing to the DWF format.
You can download the Autodesk DWG TrueView viewer and Volo View Express from www.cadstudio.cz/download and find more information about Design Review and DWG TrueView.
There are also several non-Autodesk DWG viewing applications but their results are not ideal (except for those using the official RealDWG/ObjectDBX libraries from Autodesk, like e.g. Cyco AutoManager View).
To publish, distribute and view CAD files, use rather the DWF publishing format.