Does anybody look happier when they're dancing than Solange does? The singer broke into a wide smile as she shimmied and grooved her way through "Don't Let Me Down" last night on the Late Show With David Letterman, her voluminous hair bouncing back and forth. The singer's four-piece band laid down a spare, funky groove on the song from last year's EP True, while a pair of backing vocalists, wearing mismatched vintage outfits, filled in the harmonies and added some synchronized arm movements. Letterman was certainly impressed: "Here's what we'll do," he said afterward. "We'll go on tour, all right? We'll all go on tour, like two and a half months, and I'll come out and I'll tell my jokes, then you guys will come and just kill, blow the roof off the place. And backstage it'll be horseplay." Check your local listings.