There is extraterrestrial life (why would we be so vain as to believe that we're the only life in the universe?)
I think SETI@home has a really good chance of finding something concrete, and why not donate my unused cycles for such a good cause?
SETI@home and Astropulse are funded by grants from the National Science Foundation, NASA, and donations from SETI@home volunteers. AstroPulse is funded in part by the NSF through grant AST-0307956.