DOCUMENT HINTS!
Really, make a txt file or scribble it on your hand or something. You will be a mega hero when you pull out the set of Red Dwarf on Valentines Day that she mentioned in September. Gifts with an inside joke or personal meaning mean a lot more to everyone but especially women in particular so while a lot of people might think you're a fool for getting her Death with Big Pointy Teeth, she'll remember that she mentioned that she loved Monty Python on your first date six months ago.
It might sound a bit cold or mechanical but I think that it's simply a difference of the male mind that we don't put emotional events like that into long term memory and need to augment it a bit.