Live, a few things have gobsmacked me:
1981, Rory Gallagher playing the mandolin.
~1984, Jim Lea playing Purple Haze on his bass.
2019, Tim Blake on theremin with Hawkwind.
Recordings?
There's some amazing stuff on Birds of Fire, especially when Mclaughlin trades licks with Jerry Goodman. I don't know what's going on, it's like trying to catch a flame.
Plus last night I was listening to the radio and Hendrix's All Along the Watchtower came on. The textures and sounds in that song don't sound like a musical instrument, it's more like the planes of the universe shifting against each other and letting infinity weep through.