Yes, Sir Ian McKellen is gay. He even had his "friend" at the academy awards. There were several interviews pre:FOTR that talked about how great he thought it was that a gay actor had been cast in that movie.
Most recent articles about him talk about the fact that when he's in a hotel, he rips out the page from Leviticus (in the Gideon Bibles) that calls homosexuality an "abomination."