URI

Available URI schemes

http://www.iana.org/assignments/uri-schemes.html

List of registered by IANA URI schemes

http://www.iana.org/assignments/urn-namespaces/urn-namespaces.xml

Uniform Resource Names

http://www.rfc-editor.org/rfc/rfc1738.txt

Uniform Resource Locators (URL)

http://en.wikipedia.org/wiki/URI_scheme

Wikipedia page.