How does one bake lights and only the lights (no textures, shadows, etc.) in Blender 2.67b? I don't see anything that would indicate as to baking lights within the Bake Mode.
You can render a few of the channels and mix them together later. For example, if you only want shading, you can bake shadows and AO, then mix them (using a multiply mix type) together in an image editor. If you wanted highlights as well, you could bake the specularity and mix it with the other two channels using the add mix type.