I've actually thought of learning Mingo before. Though that website hasn't been updated in forever it still has some great stuff on it.
In other news, I just bought the Cayuga Teaching Grammar
off Amazon. I'm a little disappointed there is no audio available for it (maybe just for students?). Oh well, still getting it.
þūhte mē þæt ic gesāwe syllicre trēow on lyft lædan lēohte bewunden bēama beorhtost.