These are simple regular solids that are, well, solid. They may actually use less material than the hollow dodecahedron at http://www.thingiverse.com/thing:198 if you let skeinforge do its thing. (I didn't actually check.)

These are two of the basic shapes in pyTopMod, except that it builds them edge down. If there's a way to align faces in TopMod, I didn't find it. I used blender to rotate them to be face down.

I also tried TopMod's soccer ball, but it has too much overhang and failed to build.

The whistle is in the picture because I built the plain whistle http://www.thingiverse.com/thing:1222 and built a 1cm icosahedron first and dropped it in during build.

These are pretty small (about 2-3 cm) so you might want to scale them bigger, but I think they're fine...

If you want to create them yourself, here's the procedure. Obviously, if you know how much to rotate it (like a flip) this is overkill but if you need to align an arbitrary face in blender, here's how. These instructions are a bit abbreviated, but all the steps are there. It goes pretty quick actually, it's not as complicated as it seems first time you try it.

Import the object, select and scale to suit, tab to edit, select a face, keypad * / to bring it forward and change to local mode, alt-keypad-0 to move the camera, tab and keypad-/ to finish editing and return to global, shift-rmb to add the camera to the selection, ctrl-p to make the camera parent of the object. Then keypad-7 to change to top view (or whatever alignment you want) and ctrl-alt-keypad-0 to move the camera again and the object with it. Then alt-p to unparent (and keep transformations). Note that if your object has an even number of sides, you're almost done, but if its odd, you still need to rotate it 180 about some axis to put the selected face on the bottom instead of the top. Next, go to object -> clear/apply -> apply scale/rotation data to object (or ctrl-a 1). The object is now fully modified, and you can export it as STL. (Thanks to google and http://blenderartists.org/forum/showpost.php?s=9ad363224cc626493b64a6f7290c0b0e&p=768560&postcount=7 this forum post.)