Both the DWG (AutoCAD) and STL (3D printing) CAD formats are fairly common, so finding a program capable of dwg to stl conversion should not be a problem. STL format is typically used for 3D printing purposes, which means any CAD / 3D modeling tool with support of 3D printing should also have tools to convert dwg to stl. You can even find websites that allow users to convert dwg to stl directly online.
Open DWG file Open STL fileA CAD and Gerber conversion software
A set of 3D modeling tools
An online CAD conversion service
Creo Parametric (formerly known as Pro/ENGINEER) is a complete 3D CAD software solution by PTC
A CAD converter with huge format support
A dedicated 2D/3D CAD software
A commercial online CAD converter
A 3D CAD translation software