My goodness. So much good fic. So much excellent NC-17 fic. It's like a huge candy store.
I recommend
Gertie\'s MSR Fanfic Archive as a starting point. Lots of good, romantic fic. Some sweet, some hot, some with plot, some without, of various ratings (though weighted to NC-17), etc.
I lived at that archive for a while (I was never a part of that fandom though, I lurked and read extensively).
If you want more specific recs, PM me. I got lots, but the general quality of the fics in that archive is pretty good.
ETA:
There is also the
Spooky Awards which honor excellence in all categories (including NC-17).
Sue won these under the name Suzanne Schramm, so that's a good place to start as well, since those are awesome.
alcyone