Blackfyre

I don't recall it ever being mentioned outside of the books, so it may or may not even show up this season. But odds on it being in Harry Strickland's possession?

Which got me thinking that if HS has it, that makes it the only Valyrian steel sword we know of that isn't at Winterfell (except for maybe Dark Sister, which might be at Graywater Watch) so I'm kinda thinking it would make literary sense to have the Golden Company come over and side with Dany -- just to bring that last sword north.