At LostCousins you can enter the names of your ancestors as found in the British and/or Canadian census for 1881. A basic membership, necessary for searching the database, is free and there is free access to certain census databases. The site is designed to allow users to contact others who are researching the same families - http://www.lostcousins.com/
GenesReunited is a U.K. family history site where you can search for your ancestors in 669 million family trees, census, birth, marriages, death and military records. - http://www.genesreunited.co.uk
Access to Archives/A2A is the English strand of the UK archives network - http://www.nationalarchives.gov.uk/a2a/
The WorldGenWeb Project is a non-profit, volunteer based organization dedicated to providing genealogical and historical records and resources for world-wide access - http://www.worldgenwebproject.org From the main site you can choose the region of the world and continue to refine your search to a specific geographic area.
The Olive Tree Genealogy - emphasis on Canada and U.S. - http://www.olivetreegenealogy.com/
United States
The USGenWeb Project - http://www.usgenweb.org/
FamilySearch.org - http://www.familysearch.org/en/
Family history records provided by The Church of Jesus Christ of Latter-Day Saints
Great Britain
GENUKI is one of the best sites to start your search for information from the UK and Ireland - http://www.genuki.org.uk/
The Irish Ancestral Research Association - Links to sites for Irish research - http://tiara.ie/links.html
Europe
FrancoGene: focuses on Franco-American and French-Canadian genealogy on the Internet - http://www.francogene.com/
Polish Roots - http://www.polishroots.org
DutchGenealogy.com - http://www.dutchgenealogy.com/
Italian Genealogy Home Page - http://www.daddezio.com/italgen.html
German genealogy at Genealogy.net - http://www.henealogienetz.de/genealogy.html
Other
AfriGeneas : African Ancestored Genealogy - http://www.afrigeneas.com/
JewishGen - http://www.jewishgen.org/
Quaker Corner - http://www.rootsweb.com/~quakers/index.htm
Doukhobor Genealogy - http://www.doukhobor.org/