While browsing an upcoming movie site, I found Toy Story 3 listed. I have to say found this pretty amazing considering Toy Story 2 was released in 1999.
The movie will be released in 2010, but no official release date is confirmed. The movie will be in 3D and before the release of the third movie, Pixar and Disney will be re-releasing Toy Story 1 and 2, in 3D. Actors Tom Hanks and Tim Allen have been confirmed to resume their roles as the voices of Woody and Buzz Lightyear.
I'd tell you what I know about the plot but I'm too lazy. Wikipedia gives a good idea though.
Most of this information was gathered from Wikipedia and comingsoon.net.