This is a really useful site for anything that involves manipulation of "knowledge", e.g. you can ask it what the molecular mass of a chemical is, using its colloquial name, it'll look up the formal name then work out its molecular mass. Or ask it who Batman is, it'll return Bruce Wayne!

http://www.wolframalpha.com/

Only thing that worries me is the name - if this is wolframalpha, is there a hartomega somewhere?