The Hobbit, or, There and Back Again
Balin was one of Thorin's companions on the day he happened to be outside the Lonely Mountain when Smaug arrived. He's also friendlier with Bilbo than most of the other dwarves. Balin is so amused by Bilbo's trick with the ring of invisibility (which he doesn't tell the dwarves about right away) that, when Bilbo finally does tell the dwarves about Gollum and the rest of it, Balin "[keeps] on muttering and chuckling to himself" (8.122) long into the night.
When Bilbo creeps down into the dark passage to Smaug's lair, it's Balin who accompanies him through the side door (for a little while). Balin is the one who reassures Bilbo after his semi-successful meeting with Smaug, the dragon. And Balin is the dwarf who accompanies Gandalf to see Bilbo some years after their adventures. Bilbo notices that Balin's "beard was several inches longer, and his jeweled belt was of great magnificence" (19.31). So after all of their adventures, Balin is thriving. And we're glad, because he seems like a genuinely good guy.