The Argus Clearinghouse provides access to topical guides that meet an extremely selective collection development policy. Resources are ranked according to a five-check system. Librarians might enjoy rearranging the links to appear in Dewey decimal system order. Just take a peek under Health Studies to get a feel for the enormous scope of this service. My students use this one heavily for projects on the decades, and appreciate the archive of external review links from an impressive variety of sources.
Some projects require the use of gateways.
I have found gateways especially helpful in health research. Typing the word stroke into a general search engine leads to truly disappointing results. Many of the sites students turn up will be of questionable authority. If they begin their searches in such health-specific gateway sites as NOAH or Healthfinder, they will focus their search, and guarantee themselves authoritative information and links. The same holds true for travel projects often assigned by social studies and world language teachers.