Oz - as in the Wizard of ?
Gandalf, Radagast and Saruman from Tolkien
Teiresias, the famous seer of the Greek myths
Ambrosius/(Welsh) Emrys is the historic name of Merlin (who is probably an amalgam of several historic seers from the post Roman period). Myrddin is the Welsh form of Merlin.
You could also check the Northern Lights trilogy of Pullman for more names, apart from Harry Potter.