It ends right after the Eagles rescue the clan from the frying pan and they first catch glimpse of the Lonely Mountain from way off. It was a good stopping point I think.
The second part is called The Desolation of Smaug and the final part There and Back Again. I'll have to check the book again, but obviously the next part deals with getting to the mountain and handling Smaug, and then the last part would include the strife afterwards between the Dwarves and the men of Dale - not to mention The Battle of Five Armies. Then home.