I think with the kind of 20s style private eye type that Sam represents, Michael Land pretty much nailed it with his jazz and bigband motifs from "Hit the Road". That, combined with stuff matching their current situation (taking HTR as an example, country with Conroy Bumpus or native tribe music with Bruno the Bigfoot) makes perfect sense for me.
Shirley Walker - Batman: Mask of the Phantasm Main Titles
Henry Mancini - The Pink Panther
Love Among Freaks - Kill The Sexplayer
DVDA - Now You're A Man
Ben Folds - The Secret Life of Morgan Davis
Beautiful Creatures - Kick Out
Black Kali Ma - Remain Awesome
Metallica - Fuel
AC/DC - Highway to Hell
Bad Religion - The Fast Life
NOFX - The Idiots Are Taking Over
Henry Mancini - Peter Gunn
Actually, that's a pretty fun playlist. I'm going to flip that on right now.