I know some of us see it as a "Hallmark Holiday" (like I personally do) and don't bother while a lot of us see it as a day to be romantic. Goth and romance often go hand in hand.
I figured I would come up with a
(1) A hand made card. Write something meaningful inside. If you like to write poetry, write a poem!
(2) A nice heart (anatomical) pendant. Something like this:
(3) A bat bracelet, I particularly like this one here on etsy:
(4) A nice family photo or a picture of yourself with your partner in a black picture frame
(5) This one is my favorite. While you can probably get a dozen roses for this cost, you can always send her a single black rose or you can always buy a red one and tie a black ribbon to it.