Extendible File Format


I am looking for a file format which Maya can export and I can write an importer for.

The file format needs to be able to contain the regular 3d data such as polygons, UV, materials. But I also want to be able to use multitexturing, OpenGL shader data ( for Cg or other shader ).

I could define my own file format but then I would need to write a Maya exporter. This is time consuming.