Are Pixar making Grim Fandango and Psychonauts movies? No.
Yesterday, Pixar announced a batch of new movies at CinemaCon 2012, including one based around the Dia de los Muertos - the Mexican day of the dead festivities that also inspired Grim Fandango. At the same event, John Lasseter gave a release date to a previously announced project currently called The Untitled Pixar Movie that Takes You Inside the Mind - June 19, 2015. Twitter is now afluster with pre-emptive reports that these are Grim Fandango and Psychonauts movies, but sadly the facts don't match up.
John Lasseter discussed the mind movie on the Charlie show Rose last December, and said it "takes place inside of a girl’s mind, and it is about her emotions as characters." Being set inside a single mind doesn't have much to do with the concept of Psychonauts, the point of which is to jump in and out of different people's psyches.
They've siad less about the day of the dead movie, but I'm afraid what they have said will interrupt any presumptive fandango: AceShowBiz report "Pixar confirmed that it will be an original story and not be based on any previous source material".
It would have been a hell of a thing to see. The good news is, it probably will be anyway.