I would also like to say Monaco, but somehow, I'm not so sure that'll happen this year. I've got a feeling that the hotels in the surrounding areas and fights to Nice are all sold-out. The reason I say this is because I know what the situation is like for the Canadian Grand Prix. I was smart enough to book a room for every weekend in June, because until we find out the exact date of the race, hotel rooms are fairly cheap. After that, that weekend gets blacked-out, and people are forced to pay $300+ per night.
But, if you can, definitely try to plan for the next year.