Stephen Colbert sang "Summertime" from Porgy and Bess with his guest Audra McDonald on Monday, in just the most recent of many musical moments on the Report. Colbert sings with his guests pretty often, actually, belting out numbers with Tony Bennett, James Taylor, Brian Eno, Alicia Keys — even holding his own with Plácido Domingo. (He wasn't in Company for nothing.) It's charming when Colbert sings with the pros, but it's even better when he harmonizes with them. Relive these moments, won't you?