Avatar sequels are going to flop.
I'm eager for a follow-up to Prometheus.
There was a good Aliens vs Predator book I read several years ago, too... a human ended up "hunting" with a predator, and earned a hunter's mark from the predator. I forget exactly why, but the human was en-route to the predator home world at the end of the book. I never followed up on a sequel to the book, but that would make an interesting movie, I think.
A definition of the relationship between the Engineers, the Xenomorphs, the Predators and Humans would be a great story.