A Gem of a Soul by spuffy luvr. This is a very long fic over 200k and has some darker moments but is great, a fave.
Spike has the ring in these but they have entirely different initial dynamics between them...
Normal by Kari Mouke
This is the Way the World Ends by Dark Eyed Seer.
Out of the Light by Laure Alexander is a different take, Spike has already recovered the ring where this fic starts, what Spuffyesque contact there is nonconsensual and dark and it is not a happy fic.
Buffy/Spike are already friends/together I think when Spike gets the ring in these
Half Way to Anywhere by immram
The Curse of Immortal Love by midnightjen
but I can't remember how long/if he keeps it in them.