Boolify
Teach Boolean search. Also has a compare/contrast search.
Redz
Graphical search engine.
Search Cube
Lists the sites on the square sides of a cube.
Wolfram Alpha
Search math or measurement terms. Gives all representations of it.
SweetSearch
Only searches 35,000 Web sites that have been thoroughly reviewed and evaluated by a team of Internet researchers for quality and reliability. SweetSearch excludes the junky sites that appear at the top of search results in other search engines and that waste students' time.