here is a page that compares features of different search engines.

and here is a graph of search engines by how many pages they index. It seems that in the last year, Google has pulled away significantly in the quest to be biggest. (But,,,that does NOT mean Google has everything the others have...)

which leads me to think that if you need to maximize your chances of finding an obsure term, name...etc...http://ixquick.com/ may be the way to go, as it uses all of the major engines in one search.....