The Next Big Thing

After Harry Potter we knew something else would be big, but what? Then suddenly Twilight appeared and for years captured the imagination of our world.
Now Twilight is approaching the end of its movie run and I can't help but wonder what will be the next big thing.

Do you think the next huge book will be YA? Is there room for anything else to get so big? Is there something big right now that I don't know about yet?