Hhhmmm....Ulver's "Kveldsanger" LP is great and so is Empyrium's "Where at night the woodgrouse plays"! I also have that "Weiland" 7" they put out with 3 songs on it and it's also pretty good!
I don't think I have that many (fully) acoustic songs by metal bands. I have "Mood for a day" by Yes, but that's progressive rock and not metal.
If instruments such as strings and horns counts, I have lots, but it's not metal, but more pop/filmmusic/classical/classics and so on.
I also like "Planet Caravan". I think Pantera's version is a little better than Sabbath's. It's not fully acoustic though.
Hey, that "Mine is the grandeur..." by Dark Tranquility is also pretty good and so is "Utferd" by Storm. I suspect the latter to be jacked from an old folk song, as "Kings Selma" by Hedningarna sounds a little similar and it says it's a traditional song in the cover.