COLLADA is the closest thing to a standard file format, directly supported by just about everyone. The downside is that files will be big and load times will probably be slow.  There is a runtime format in the works (I can't seem to find the link right now) but it is not done yet. If I write my own parser I could support binary data stored in external files via an href attribute or similar. I imagine the runtime format will use something similar to this anyway.

I could also use a simple format (like Wavefront) to get up and running, and then switch to the COLLADA runtime format when it becomes public.

If nothing else comes along, the .x format of Direct3D might not be a bad standard to use.