Yale University's Research Guide to Modern European History is particularly good on history by region.
The American Historical Association's page with of affiliate historical organizations.
Internet History Sourcebook Project Collections of sources for ancient, medieval, modern, etc. history. A convenient way to find the classic sources of a period. Be wary. "Editions" and translations contributed by volunteers can be outdated and error-ridden.
The Voice of the Shuttle covers all periods of history. Digitized video collections were recently added.