*Indicates books I personally have not read, but which have been recommended to me by friends, or found and presented here out of potential interest. Please feel free to add suggestions in the comments below!
All links go to Amazon, since they have the very best prices for used books in good condition.
The Picture of Dorian Grey by Oscar Wilde
Eerily eloquent tale of a young man whose portrait ages rather than his skin, and his inevitably gruesome demise...
Sabriel, Lirael, and Abhorsen by Garth Nix
Brilliantly written trilogy dealing with the dark magick, mostly necromancy, and the concept of its use both for Evil and for Good.
I Am Morgan le Fey, I Am Mordred by Nancy Springer
Beautiful, dark tales of romance and magick. Re-imagined stories from the perspectives of these notorious characters. Similar to the Mists, they are not shown as villains.
The Mists of Avalon by Marion Zimmer Bradley
An epic retelling of Arthurian folklore. FILLED with magickal and spiritual wisdom. I often refer to this as "the witch's bible." It is well over a thousand pages, and my copy (which I've had since i was thirteen) is almost completely underlined, dog-earred, with a separate book's worth of notes in the margins. A profoundly worthy investment, I give you my word :D
Practical Magic by Alice Hoffman
The modern story of two sisters, and their magickal lives as natural witches. Made into a movie with Sandra Bullock and Nicole Kidman. Trust me, the book is a millllllion times better...
The Girl with the Dragon Tattoo, The Girl who Played with Fire, The Girl who Kicked the Hornet's Nest by Stieg Larsson
Epically amazing story of a goth hacker social outcast who works for a security company and later helps a journalist with several murder cases. The movie is amazing, but yes, the books are better ;)
Confessions of an Ugly Stepsister, Mirror Mirror, and Wicked by Gregory Maguire
I have always loved his dark, satirical rewriting of classic faerie tales (fun side note, I got Confessions, the Mists and Crimson Petal on the same day), with political references and relevant social plots. His work is genius. The musical "Wicked" is shit, and completely and totally different from the book, I promise.
The Crimson Petal and the White by Michael Faber
I adore this book. It is the story of a prostitute in Victorian England who begins as the lowest of the low, and then finds a wealthy, married patron who takes her on as a kept woman. It isn't exactly a love story, however... ;) A heavy read, but dark and erotic.
Of course this is a goth classic... Unfortunately, she has denounced her old "evil" tales in favour of reverting back to the Catholic mindset she knew as a child. So sadly, her new books aren't half as good. But we can still honour the old days... the mystifying words remain the same.
Also check out her New Tales of the Vampires. I haven't read Vittorio, but Pandora is amazing.