Personally, I think flowers are nice, a dinner out is fun, lingerie is also nice, but only if you have been dating for 6 months or longer and know what size she wears.
I've also recieved a good book as a gift for V-day and loved that.
Personally, I think cards are dumb unless you get a blank one and actually write something real - the idea of hallmark speaking for you is cheesy and sad. Funny one can be cute though - if they really are funny.
But, if she doesn't get you anything, I would take that as a red flag if you have been dating seriously (read: exclusive) for more than 3 months.