The James Webb Space Telescope (JWST) is a large infrared telescope with a 6.5 meter primary mirror. This telescope will eventually replace the Hubble Telescope. The Webb Telescope is a good deal larger and should be able to provide significantly better images than the magnificent images seen from the Hubble.
Here's a quick run down of the specs:
Despite the inevitable coolness of this telescope, the project is having some trouble. It is currently over budget by about $1.5 billion dollars over the previous $5 billion dollar budget, which itself was a $1.5 billion over run from the original 3 billion. The telescope is a little behind schedule, too. The project was originally supposed to launch in 2007, but now the estimated earliest launch date is 2015. Part of the reason for the difficulty is that the Webb telescope cannot be serviced by the space shuttle like the Hubble telescope. That means there isn't really any margin for pre-launch error.