I only have Nirvana - "Unplugged" on vinyl. It's pretty good, if you are a Nirvana fan (I'm not much of a fan).
I have "The Unplugged Collection, Volume One" on CD as well. It's a collection of songs, one from each artist, from the early Unplugged sessions. There are some really good tracks in the collection. My favorite might be - Elvis Costello "Deep Dark Truthful Mirror".
If you want to hear a really great acoustic album, from a modern electric rock band, check out - Band of Horses - "Acoustic at the Ryman". I find the acoustic arrangements of the chosen selections to be fantastic.