Well, most of us make our own 3Ds for our coasters. You can use the Object Creator, which is in unregistered versions only, Wings 3D, which is completely free, and has tons of features, Google Sketchup (~$500 for 3Ds exporting capabilities), 3Ds Max (~$2000-$3000 for entire program), and other various object creating programs.
Hates oscar for taking points...