ShapeToDxf (US$49.99) is a program which takes Esri shape files and converts them into AutoCAD DXF files. The program is very easy to use, just drag the SHP file into the main window (or open it with the SHP icon) then click on the DXF icon to save it.
You get to preview the DXF before saving it. In fact ShapeToDxf can be used as a shape file viewer:
You can choose to have the objects in the SHP file assigned to different layers according to their database values (if there is an accompanying DBF file).
For example geological shape/dbf files sometimes contain comments about geological formations or hazards. You can choose to have these hazard warnings appear as text in the DXF file on their own layers:
Differences in geology and other information can become immediately clear when using the layer by DBF field option:
ShapeToDxf also allows you to assign the objects to different layers (with different colors) according to their elevation or z height. This gives you an immediate idea of the relative levels of the objects, even when viewing in 2D:
For 3D Esri files (or 2D Esri files with DBF files which contain elevation data) the output DXF is a 3D DXF.
The program also has a simple 3D viewer includes so you can get an idea of the elevations of the objects before saving the DXF file:
When the SHP file contains a collection of point objects they can be saved in the DXF file as AutoCAD point objects, or as symbol blocks. There are 17 symbol types, like circle, cross, drillhole, plus etc. AutoCAD experts can design their own symbol blocks and add them into ShapeToDxf.
Here are two further screenshots, the first shows part of Faults500.shp (Kentucky) as viewed inside ShapeToDxf...
and this screenshot shows the DXF file produced by ShapeToDxf when viewed inside AutoCAD...
And here's a quick guide for how to make fields in the DBF file appear in the DXF file:
Double clicking on the name of the field, in the first column, you can change whether the text is exported to the DXF file, it's size, layer and color. A comprehensive help file is available here, and more screenshots are here.