Many news sources are reporting on Robert Pattinson having cut his hair (shocking!), and on a recent appearance on the Ellen Show, he confirmed it was for Water For Elephants. He also stated that work on the film starts today – May 20th – in Los Angeles, and photos can be seen at Celebrity-Gossip.net of him on the set today. No sign of Reese yet, but I will keep my eyes out and post the first set photos as soon as I find any! Feel free to post a comment here if you come across any.

‘It’s about a circus in the 1930s based on a book called Water for Elephants with Reese Witherspoon’.
– Robert Pattinson on Water for Elephants

EDIT: I’ve been looking for more details, and come across a video of Reese talking about the project, and a further quote from Robert Pattinson.

“It’s set in the Depression era, when circuses traveled by train and this guy runs away and jumps on a train to be a hobo and by accident, he doesnt realize it’s a circus train. He becomes part of this world because he has no life to go back to and ends up falling in love with the ringmaster’s wife, played by Reese Witherspoon. The ringmaster just happens to be kind of a schizophrenic as well. He’s a most charismatic and terrifying person. He’s Christoph Waltz from Inglourious Basterds. I did a read through yesterday with him. He was sitting right next to me. It was a little terrifying.”
– Robert Pattinson