By now everyone has probably heard of the free 3D architecture app available: google sketchup.
Until now it has only been possible to create white lines, but with a simple modification of the DXF export script 24-bit colored scenes can be created. Right now the update for ILD SOS supports this, and LaserBoy probably will in the future as well.
Just unzip the attached file into the sketchup/Plugins directory. Color the faces of the objects you want to, and select Plugins/Export DXF to save the DXF file. Thanks to TL for initially suggesting the use of 420 DXF color code.
Also attached is a 3D ilda file that can be imported into laserboy and spun around to see the whole scene. This file is not meant to be played directly.
Note that, unlike 3DS Max and the illustrate! plugin, this method will generate see-through objects with visible rear lines. Also currently there is no way to animate scenes in Sketchup like there is with 3DS Max.