Jay Z may have 99 problems, but taking the subway ain't one. The 'Holy Grail' rapper hopped on the London Underground this week and headed to his concert at London's O2 Arena. He wasn't alone; tour opener/producer Timbaland and Coldplay's Chris Martin were part of the entourage. But these guys aren't the only ones that ride the subway to shows. Check out the other celebs that prefer public transport from time to time.