From the ScienceDaily release:
Shuttle astronauts will make one final house call to NASA's Hubble Space Telescope as part of a mission to extend and improve the observatory's capabilities through 2013.
The flight is tentatively targeted for launch during the spring to fall of 2008. Mission planners are working to determine the best location and vehicle in the manifest to support the needs of Hubble while minimizing impact to International Space Station assembly. The planners are investigating the best way to support a launch on need mission for the Hubble flight. The present option will keep Launch Pad 39-B at the Kennedy Space Center, Fla., available for such a rescue flight should it be necessary.
There will be a lot for the astronauts to do on this servicing mission. Two new cameras are to be installed, gyroscope and battery replacement and an attempt to repair the Space Telescope Imaging Spectrograph are among many tasks to do.
This last mission should allow Hubble to operate at least until 2013 and fill in the gap until the James Webb telescope goes online.