Well, its not really a search engine, it is a “computational knowledge engine,” but I will just say search engine since you are searching the knowledge base for things. WolfRam|Alpha officially launched yesterday and it is really quite amazing. Type in a word or query and WolfRam|Alpha spits out what it knows about it. My first name for instance came back with information on rank, fraction of people with that name, years it was popular, the age of others with that name, etc.
But, the real power comes when you begin combining queries to do things like math equations, stock comparisons, or sports comparisons. I think the real value of something like this would be if they offer an API for programmers to call for real time information. Oh, wait, I just looked and they are doing that too!