Maybe too obvious: Nicole Scherzinger from Pussycat Dolls. But she’ probably more a fan of a certain driver, than of the sport.
I’d emphasize Eric Clapton. He’s been spotted by Martin Brundle during the grid walk on a number of occasions already.
Former athlete Michael Johnson is a fan of racing in general, including F1.
Read somewhere on the internet that Ah’nuld Schwarzennegger apparently watches each F1 GP on TV as well.