I'm behind on my Weeds watching, but they're doing a fun thing with the theme, Little Boxes. Throughout season one, it was Malvina Reynolds, who wrote the song in 1962.
My DVD watching is stuck there, but for season two and three I can look forward to a variety of artists, including:
Death Cab for Cutie:
Jenny Lewis with Johnathan Rice:
Others coming up include The Shins, The Decemberists, and Billy Bob Thornton.