This one's pretty narrow in focus, but that also means it runs deep. The Eighth Century and All That I just discovered it. The site is maintained by a scholar, so it cites its sources. You can rely on the information you find there. He has been writing posts for at least four years, and there are a great many articles, not only on politics but on society, culture, etc. If you are looking for early medieval material (Charlemagne, etc.) you need to put this one on your list of resources.