The only one I know and remember is Vanilla's story: 'World Spins Madly On'
Summary: One slight mistake in a spell intended to re-soul Angelus lands Buffy in an alternate universe where no one is who they should be, and nothing makes sense. She's desperate to return to her home, but when she starts to fall for her new Watcher, William Pratt, she begins to wonder where she really belongs. AU after the events of Innocence.
http://spikeluver.com/SpuffyRealm/viewstory.php?sid=29837&warning=NC-17So it isn't Spike being the watcher.