Dogpile (free)
Searches multiple engines (Google, Bing, Yahoo, Ask) at the
same time.
GluedIdeas (free)
A source for free encyclopedias, authoritative historical reference texts, guidebooks, learning manuals and other documents.
Mocavo (free; memberships available)
Mocavo is the world's largest genealogy search engine with
more than 6 billion names in the index. On Mocavo, users can search
across millions of family history resources from one centralized
website.
AncestorSearch (free)
Randy Majors created this custom search using Google.
The search returns a more focused set of results by using
advanced Google search techniques including exact phrases, forward
and reverse name order, alternate name spellings, logical
operators, and so on. Try it, you'll like it!