I asked the question over at Astro's as to when the next space based telescope would be going up. Well, I didn't want to wait so I looked it up for myself. Turns out that one is planned for launch this year.
The Herschel Space Observatory is scheduled for 2007 and is a cooperative effort between 10 countries, including the US. Herschel will be able to scan the heavens for infrared light, which is very difficult to do from earth due to the atmosphere.
In 2009 WISE, or Wide-field Infrared Survey Explorer, is expected to launch. WISE's mission will be to map the sky in infrared light searching for the closest and coolest stars, the origin of stellar and planetary systems, and the most luminous galaxies in the Universe. Apparently the design was just approved and is going to final design and construction.