Regesta Imperii. The “central node,” so to speak, for research on medieval Germany. Outstanding resource for digitized and cataloged imperial registers, as well as a first-rate, constantly updated bibliography.
Monumenta Germaniae Historica, digital editions. Digital editions of the (mostly) Latin chronicles in the MGH collection.
Mediaevum.de. A clearing-house of German resources for medieval studies, including digitized manuscripts, dictionaries, degree programs, you name it. Happy browsing!
H-Soz-Kult. Review of Knut Görich, Die Ehre Friedrich Barbarossas.
William Urban, Tannnenberg, Chapter 1
Analecta Praemonstratensia, 2011. Has abstract for Michael Oberweis’ article on Burchard von Ursberg.