Ooh, I got here by vanity googling - I write/wrote for Black Lace too, Alurkatsoftplay! - and am thrilled to hear of people looking for good erotica. Maybe I can help ...
I wanted to suggest that anthologies are a great way to find new authors, get a taste of lots of different writers at once. As well as Black Lace, the Mammoth books are good for a kind of more literary slanted erotica. There's also Harlequin Spice - more romantic, as you'd expect. In fact there are loads of epubs - Ellora's Cave, and lots of wee small indie ones. Cleis Press do a lot of interesting anthos with a very inclusive attitude to sexuality.
For the classics there are Georges Bataille (pretty out-there. Very ... European), Henry Miller (I never really considered this erotica), yes, Nin (Delta of Venus and Little Birds), Venus in Furs, The Story of O.
I am trying very hard to be informative and not push only my favourites and my publishers - inevitably it's hard! There is a tonne out there, and I expect there will shortly be a tonne more since FSOG.
:) If anyone needs any more specific pointers, though, (ahem) happy to help.