I would buy the Neverland Ranch, get plastic surgery and become Michael Jackson!
Just kidding. I would improve my lifestyle and that of my relatives in all the usual ways (hopefully nothong too outrageous, but definitely enjoy it) and then set up a charitable foundation for what purpose? Hard to decide. But probably focusing on worldwide child health and education issues as well as AIDS prevention. The needs of child tsunami victums would be high on the list. A donation to CPF would not be overlooked, either.
By the way, before I sound like a generous person, I have to admit that if I won only a million dollars, I am stingy enough that I probably wouldn't share a penny of it, but a billion is more than I could ever spend, so doing something good with it is not very painful.