The Thirteenth century Austrian epic familiar to all fans of Wagner's Ring Cycle.
This is a great source if, and only if, you speak German. Hartmann von Aue wrote a version of Iwein which would be an interesting slant on the Troyes version, but as far as I can find, there aren't any English translations of von Aue. If you see one however, snap it up, tell from me, and e-mail me the Bibliographic information.
Another great Arthurian epic by Wolfram von Eschenbach. I couldn't find any online English translations, but Amazon certainly has plenty of versions. Make certain you get an actual translation of the period epic and not a modern re-telling.