At present there are 28 projects you can donate your computer time to.
I used to be a member of the SETI program many years ago and have recently rejoined it. What it does is use my computer to analyze information from the Arecibo radio antenna in the search for extraterrestrial intelligence. However, there are goals far more noble such as processing genetic information in diseases and doing research into quantum physics.
If interested, pay a visit to BOINC and consider using your computer for something other than games. You just may play an important role in a new breakthrough.