INTERNATIONAL:
The next few sites tend to share information
http://worldconnect.rootsweb.com/

Ancestry has a free trial going at the moment for their English and Irish records. But when you need to cancel you are best to do it by phone, as they take a long time to cancel by email and you may get charged the full subscription fee. Lots of info there.
www.Ancestry.com

Family Search - Jesus Christ of Latter Day Saints. Has info from all over the world. Lists the 1881 British Census, and the International Genealogy Index. Some information in uploaded by individuals, and so it is always best to double check the information you gain. Allows you to download the GEDCOM Viewer, which is one method of creating your own family tree to enable you to upload it to the web site.
www.familysearch.org

Commonwealth War Graves Commission - Personnel who died in WW1 and WW2.
www.cwgcsearch

It offers a free 7-day trial, membership costs US$74.95 per year. Will allow you to create your own family tree, which is displayed, on-line, and link you up with anybody else who has input the same people, thus enabling you to view their full tree. It is a US based site, and to benefit fully you will need to input your family tree. It will also show you some famous people's family trees.
www.onegreatfamily.com