DJ Noodles and Nic Balz put out this gem of a mashup, and surprisingly it didn't get much attention. Using Jay's accapellas from The Black Album (and some from Jay's MTV Unplugged show) with the music of Nirvana's MTV Unplugged they created an actual mixtape that bears listening to more than once or twice.
All the links online I've found were dead, so I fortunately got my hands on a copy of this, thanks to a friend of mine. Feel free to share this with anyone you think might like this.
***11/22/12 NEW LINK***
DOWNLOAD MIXTAPE HERE
01. Encore b/w "About a Girl"
02. Intro b/w "H to the Izzo"
03. Dirt of your Shoulders b/w "Lake of Fire"
04. Change Clothes feat. Pharell b/w "Jesus Doesn't Want Me For A Sunbeam"
05. What More Can I Say? b/w "All Apologies"
06. P.S.A. b/w "Come as you Are"
07. Threats b/w "Plateau"
08. 99 Problems b/w "The Man Who Sold The World"
09. December 4th b/w "Pennyroyal Tea"