Rihanna’s tour is the latest to be hampered by poor ticket sales this summer. According to Live Nation, Rihanna — who is out on the road with Ke$ha and Travie McCoy — has had to cancel dates in Denver, Indianapolis, Phoenix, Dallas, and Atlanta on her Last Girl on Earth tour. Not all tours are struggling, though — the acts selling well this summer read like a Twihard’s “favorite music†list on Facebook: Lady Gaga, Justin Bieber, Muse, Taylor Swift … and, um, James Taylor with Carole King. [MTV]