I use several programs to develop my models, but primarily:
- Corel X3
- Truespace 7.6
OpenSCAD is great for developing "mathematical" models such as the Log Church, the GasPumps, or the Container Chassis models. It works the way I think.. rather than drawing with the mouse, you code the objects using a C++ type language. If you need to do something repetively... there's a for..next loop that makes it easy. Example: the Ships Propellers I designed took only about 15 minutes of coding. Check openscad.org for the latest version.
I use Corel X3 to convert raster drawings to vector drawings. That's a whole topic by itself.. click here.
For more complicated, organic, or what I call "curvey" models, I revert to Truespace. It's a classical 3D "drawing" program, much the same as Autocad, Blender and the other tools that are out there. As it happens, I've used Truespace for 20 years now, all the way back to the original version.
In 2008, Microsoft bought Caligari and turned Truespace into a free download. The small trap to this is that they then updated to version 7.6.1 which removed the STL output option you need for Shapeways. If you want to try TrueSpace, you need version 7.6, not 7.6.1
The correct version can still be obtained here.
Another group of designers has been successful using Google Sketchup for designing. It "works", but you have to add-on one of several STL Exporters to it.
Here's a list of 25 free designing tools: