Good for you, Daniel! Your girlfriend is going to love this
As to specific suggestions, I think the important thing is that you do something that makes her feel special and lets her know that your relationship with her is really important to you. It doesn't matter how much money you spend on it ... what matters that it doesn't seem too contrived and that it comes from your heart.
Here are some quick thoughts:
-- write her a poem and put it in a special card
-- designate a day where she's "queen for a day", where she gets her way in everything
-- have a date at a weird hour, like 3:00 in the morning or something ... take her to an all-night cafe for breakfast
-- take her to lover's lane to watch the sunset, then make out like crazy
-- get a book of love poetry and read it to her in bed
-- sing to her ... a man once sat on the edge of my bed with his guitar and sang to me after we'd made love ... could he sing? heck no, but it was so sweet it brought tears to my eyes
-- hide a bottle of wine and a couple of wine glasses in a park or beach, etc ... take her for a walk in the moonlight to where the bottle is hidden
-- take her window-shopping for an afternoon ... women love that ... make sure you hold her hand and display enough physical affection that anyone looking at you can see how you feel about her
-- be her sex slave for an entire evening
-- and the old stand-by ... send her flowers at work
Good luck to you
Hayley