STL to DXF Batch Converter - free software
I created an Excel VBA Macro that converts Stereolitography STL files (ASCII format) into AutoCAD DXF files (again, ASCII format). It can convert multiple files in a single run.
You can find the program in the solvengineer.com Codes page.
A free and easy way to create STL files is to build a model in Google Sketchup and export it to an STL file via an STL export plugin.
You can download a free DXF viewer, EDrawings 2008, here.
Enjoy!