The James Webb Space Telescope is to be Hubble's replacement after 2013. Take a look at its progress here.
   
European HST website, lots of great resources
   
Lots of formal versions of the activities listed here, plus more NASA HST (& our) educational resources
   
Sun|Trek website, lots of classroom resources based on the Sun and the SOHO mission.
   
South African Astronomical Observatory & Southern African Large Telescope homepage
   
The Faulkes telescope website, now schools can signup for FREE sessions to use the telescopes.
   
NASA's Keplar mission to find Earth size habitable planets. There is information on Johannes Kepler and other PowerPoint files in the education section.
   
Information explaining the gold disc aboard the Voyager probes containing a message to aliens.