According to The HMSS Weblog Javier Bardem confirmed last week that he has signed for Bond 23. The short article states:
Javier Bardem, in a segment last week on ABC’s Nightline, confirmed he’s playing a villain in Bond 23. He said it will be “fun” while “I cannot tell you many details about that.”
The article provides a link to ABC Nightline, where you can watch the video clip in which Bardem makes the announcement; however, it appears access is blocked to anyone outside the USA.