Christopher Nolan is already planning his follow up to Batman: The Dark Knight Rises and it is reportedly another Howard Hughes biopic, following Martin Scorcese's 2004 The Aviator. However as reported by NYmag this one will focus more "on the freakier decades of Hughes remarkably secretive and OCD-addled life".
The blog give some details on the project:
"We'll meet the Howard Hughes who spent much of 1948 sitting naked in a bungalow at the Beverly Hills Hotel with only a pink dinner napkin covering his genitals as he screened movies from his studio, RKO Pictures, and ran up an $11 million tab; the Hughes who — obsessed with food safety — once bought every franchise restaurant chain in his home state of Texas, and who was similarly so concerned about air quality that he installed an aircraft filtration system in his 1954 Chrysler New Yorker, taking up its entire trunk; the Howard Hughes who had his hair cut and nails trimmed only once a year, and who was seemingly as addicted to Baskin Robbins Banana Ripple ice cream as he was to regular codeine injections; the Hughes who at the end of his life considered only Mormons trustworthy enough to be let into his inner circle."
Nolan has been quoted previously via IMDB: "Following Insomnia, his next project was going to be a Howard Hughes biopic starring Jim Carrey. Nolan had the screenplay written calling it "one of the best things I've ever written" but he never made it thanks to The Aviator."