I'll toss in a vote for Clopin, even though he's anything but a prince. Maybe a prince of gypsies. That guy can sure hit the high notes: "Sing the bells, bells, bells, bells, bells, BEEEEELLS OF NOTRE DAAAAAAAME!"
And Gaston is one of my favorites, too. Partly because he has such a great voice, and partly because he's just so darn funny. "I'm especially good at expectorating... ptooey!"
And Beast, probably the only one in my list who qualifies, being a prince and all. A shame we don't get to hear more singing out of him.