I just read an article on the World Science website about the potential for lifeforms to exist that do not rely on carbon or even water. Scientists think the possibility of life based on these other materials is likely, and are now testing the properties of known elements and compounds to see whether they can find anything else that might be suitable for life - and if so, where in the universe the right amounts of these materials exist.

http://www.world-science.net/othernews/090922_lifeforms.htm

Perhaps the little green aliens will be even more alien than we thought...