One of my favorites is Jesse Ed Davis' solo on Jackson Browne's "Doctor My Eyes". He was brought in as a session guy to play lead guitar on the song, which was partially finished. He listened to the cut twice, then he played the lead guitar on it, including the solo, then he put the guitar back in its case and left. It's one of my favorite guitar slinger stories. David Crosby and Graham Nash are singing backup as well.
Jesse Ed also gets credit for Duane Allman taking up slide guitar. He played lead for Taj Mahal early on, and Duane heard them do "Statesboro Blues" in 1967 with Jesse Ed on the slide. That was the trigger for Duane taking up both the slide and that song. He also played on Dylan's "When I Paint My Masterpiece" and "Watching the River Flow", and appeared at the George Harrison's Concert for Bangladesh.