eDrawings by SolidWorks Corporation has been on the Mac for years now and it has been an excellent way to view Autodesk DWG and DXF files in particular. This was before the return of a native AutoCAD for the Mac.
Now SolidWorks has released eDrawings for the iPad. eDrawings for the iPad is the only CAD viewer on the iPad that allows you to view native eDrawings files as well as native SolidWorks parts, assemblies and drawings files.
Multi-touch gestures let you pan, zoom, and rotate models easily. You open files from email, iTunes File Sharing or an internal network. You can view 3D animations, 3D static views and 2D drawing views.