The request we received most often was to support the STL file format. Being the granddaddy of file formats in rapid manufacturing, almost every 3D design application can export STL. As of today, Shapeways also accepts these files.
This will make it MUCH easier to get your design on Shapeways as you'll no longer have to rely on a third-party application to convert the files.
When uploading STL files, please note that we're assuming a base unit of 1m. This is non-standard; most applications assume either 1 inch or 1 mm. We'll add an option for that later, but for now just take care that you scale your object down before exporting it.
While most 3d design applications support STL, some CAD apps don't. In this case I can recommend MeshLab, a free Open Source cross-platform (Windows, Mac, Linux) tool that will do the job for you. To see if your application can export to STL, check our table of Supported Applications.
Does STL do the trick for you, or is there another file format that you would much rather work with?