The heart of the Mountain; The Arkenstone. Also a lot of gold
Bilbo gave the Arkenstone to Bard so he could use it to stop a battle between the Elves, Men, and Dwarves. It did not work.
Bilbo takes possession of the Arkenstone without telling Thorin.
Bilbo took the dwarven jewel, the Arkenstone.
He retrieves it when he is escaping Smaug
Bilbo took the Arkenstone. It was the treasure Thorin desired most.
Bilbo claimed that under the terms of the contract he was due a proportion of the dragon's treasure, and that he had taken the Arkenstone as his share.
Bilbo offers the Arkenstone to Bard and the ElvenKing
Bilbo finds and keeps a gem called Arkenstone.
Bilbo took the Arkenstone from Smaug's treasure trove. He gave it to the men to use as a negotiating tool.