This addon by Andreas Esau allows you to UV map multiple separate objects at once, packing the resulting UV in one texture.
I am currently working on a character in blender and needed to combine multiple objects into one uv layout. Well blender has its problems with handling multiple objects uvs at once. I have written a small addon for that exact purpose and tried to integrate it seamlessly into blenders workflow. Another small step to improve the workflow in blender. Now you just select all the mesh objects you want to edit the uvs and press the new appearing operator in the object tools. Press it, edit everything as you wish and tab out into object mode again. Thats it. The addon handles everything in the background for you and copies uvs to the objects.
I know there is the texture atlas addon, which has may also have extended functionality. But I tried to go for a different approach here. I wanted to make this as best integrated in blenders workflow as possible. The texture atlas addon needs some setup beforehand and this makes it a bit more complicated.