What kind of book should I write?

I've seen many people who ask questions worrying about whether the idea for their story is "done to death" or not, and sometimes it makes me a little sad. The point of writing is not to publish a book and become a bestseller--it's to write because you love it. Instead of focusing on whether or not your novel will bring you money or fame, just write what you love to write. If vampires or fantasy are your pion, then write about them! Don't let anyone tell you what is overdone or stupid; if you care enough about what you're writing, other people will see that and care too.