It kills me whenever people say "Happy Belated Birthday." That isn't correct. The birthday isn't belated; the greeting is belated. Since "Happy Birthday" can be considered the greeting, you should say "Belated Happy Birthday."
This has been bugging me for years. I wish I could put an end to it, but it's going to keep on going much like "same difference," "anyways" and "could care less." Ugghhhh.