Recently I was listening to a singles collection by the Zombies, and I paid special attention to two B-sides from 1966 written by singer Colin Blunstone. As far as I know, those were the only two official Zombies' songs written by Blunstone, while keyboardist Rod Argent and bassist Chris White wrote almost every original song of the band. I had already listened to those two songs several times before, but I'm still surprised because I really like both tracks by this unusual songwriter. These are the songs:
Maybe the good performances also helped a lot.
I can't think of many other examples of good quality songs written by unusual songwriters to be included in a record by the band they were part of. "Octopus's Garden" is an obvious example. Then we have "In Another Land" by bassist Bill Wyman, included in the Rolling Stones' album
Their Satanic Majesties Request (they even put an asterisk on the song in the back cover, indicating
The Rolling Stones except *Bill Wyman). The song is not a big triumph anyway, just a decent psychedelic track.
It has been much worse in other cases. This was one of the very few contributions by singer Roger Daltrey to the Who catalog, and it's pretty poor:
As another example, Jefferson Airplane's drummer Spencer Dryden wrote this weak country-rock tune:
Can you mention other songs by unusual songwriters?