Family Guy.
Music plays a big part in the show. Not only does the show have some great original songs (the barbarshop quartet explaining what a vasectomy is) but they pay a LOT of money to sample other songs, and have their own orchestra learn the music for it (Peter playing on the Patriots, getting a touchdown and singing Shipoopi from The Music Man).
One episode had Frank Sinatra, Jr. do a guest spot. Various parts of Frank Jr., Brian and Stewie singing.
Brian and Stewie often sing songs together. They did musical numbers in both Rhode to Rhode Island and Rhode to Europe. (And in Road to Rupert, there was a clip of Stewie singing and then later 'tap dancing' with Gene Kelly.)
The Simpsons used to do that. They had a lot of great original songs. (If you're not careful, you'd find yourself absentmindedly humming them). But not so much anymore. Now Family Guy (and American Dad! more and more) are the more 'musical' shows.