I found it very impressive this O3D API by Google. You can change and create 3D objects in your browser with Javascript code.
There are plugins for various browsers (Windows and Mac by now). I will have to compile it in order to run the samples on my Ubuntu, and I want to do it soon. :)
I'm looking forward to see its applications' speed and size, but it pretty looks good and fast on YouTube. The technical details mention the import process of COLLADA files, and points to some 3D apps capable of exporting files to this format. I don't know why they didn't mention Blender, since it has a COLLADA exporter for a very good while.