Cyndi’s List
One of the most extensive genealogical sites on the web

Distant Cousin
An online archive of genealogy records and scanned images of historical documents from a wide variety of sources, such as newspaper obituaries, city directories, census records, ship lists, school yearbooks, military records, and more. In all there are more than 6 million genealogy records from over 1,500 sources online.

Foreign Business Directories -Searchable online.

Genealogy Indexer
Search 77,000 pages of historical directories (business, address, telephone, etc.), 28,000 pages of 64 yizkor books (memorials to Jewish communities destroyed during the Holocaust), and 7,000 pages of lists of Polish military officers. Most of the directories are from Poland, Galicia, or Romania.

Tufts University
Tufts University: Boston City Directories.