Hubble's replacement, the James Webb Space Telescope, is scheduled to be ready for 2011. It's not going to orbit the earth, it is going to instead be in a spot where it is 'trapped' between the earth and the sun- a Lagrange point. It is going to have a beryllium mirror 6 times larger than Hubble's. It is also going to be specialized for viewing in the infrared, which is something you just can't do on earth as the atmosphere blocks those wavelengths.
http://www.jwst.nasa.gov/FAQ/FAQ.htm