The first book I ever read with gay characters was a children's book my aunt gave me when I was in my early teens. It had no description on the back so I don't even know if she was truly aware of what it was about (something I've always wondered considering some of the views on homosexuality I've seen in family).
It was called '
Living in Secret. It's nowhere near the best book I've read but I thought it dealt with some of the reality of living with a gay parent (and questioning one's own sexuality) in a good way for pre-teens and those in their early teens. It does focus heavily on it, though.
I don't have a library card (*cough* hefty fine) and am limited in cash so I haven't really read too many published books dealing with gay characters. I certainly would be interested in doing so.