The sole ending musics I can remember right now are the ending music of Monkey Island 1, which became Elaine's theme music in MI2, and the begining of the ending music of Indy and the Fate of Atlantis, the calm music on the sunset, and then Indy's theme kick in and the credits roll on, just like in a movie, the rest of the music is so-so but this part is awesome. I'll see if I can remember more tomorrow.
Oh, of course, Portal!
Edit: I searched but the only other memorable ending music I could think of was the ending music of the Machine level of Knytt Stories. It's not an adventure game, but it's in my opinion what every video game endings should aspire to be.