Kris Kristofferson is the best cross-over artist. Better than Henry Rollins, even!
First Kris got kind of famous when he was in Sports Illustrated for being really good at rugby, us football and track and field. Then he got his degree in literature and became a Rhodes Scholar at Oxford, earning another degree, went into the army and became a captain and I guess a ranger. West Point wanted him to be a professor of English literature but the dude was way too cool for that and decided to become a musician instead. Then he became kind of famous for writing a shit ton of really fucking great songs, such as Me and Bobby McGee and Sunday Morning Coming Down (which is the Best Song), but other artists made the songs famous when they sang him. Then he started getting famous from singing his own songs, then was in the country music supergroup (no other supergroup is better) The Highwaymen, and was also in a bunch of movies too.
Tom Waits is also very good both as a singer-songwriter and actor. He's also apparently really good at suing companies.
I also would be considered a fan of She & Him, and only partly because of my crush on Zooey.
Basically you can be a crossover and be awesome if you are a total fucking badass.
(PS: thank you for mentioning Dead Man's Bones on here... I'm listening on myspace and the music is really awesome)