Fordham University provides a list of links to online primary sources from the medieval era.
British History Online contains primary and secondary sources for the history of the British Isles. You can find a diverse range of sources here.
A website offering a range of academic and popular articles regarding the Middle Ages.
An online academic database used by universities worldwide that is a superb resource for History students. To view full articles, you will require membership.
This searches internet sites for academic articles and books. It often only provides one or two pages, but it is often enough to find quotes and bibliographical details.