The main (re)mixes I currently have:
Garbage - Who's gonna ride your wild horses (Bono on Vocal)
U2/Depeche Mode switching singers on So Cruel (Bono starts with Depeche, then U2 with Dave Gahan takes over)
Nine inch Nails - Zoo Station (Trent/Bono on Vocals)
U2 - Ultraviolet 1 (Hansa demo with parts of Spinning Head, The Fly, UV Light my way and one "easter egg" weaved in)
U2 - Zoo Station as it could have been (mix of Sky Down, Baby version, and the Eno "Bottoms" remix)
U2 vs. A-ha (The sun always shines on tv mixed with Beatiful Day)
Nine inch Nails - Hurt (NiN version with Johnny Cash on Vocal)
Johnny Cash version of "One" (with Bono on vocals), and the U2 version (with Cash on vocals)
I have more, but these are actually "listenable" at the moment
I'm still in the phase of learning about mastering so these remixes might get updated with newer, better sounding versions. If anyone has ideas or their own creations, please join in on the fun.Thought to start off with a new (re)mix of Johnny Cash joining U2 on "One". It's Cash and Bono altering vocals and Cash's guitar joining U2's guitar intro: