Woman differ in the romantic since. You could always stick to flowers and roses or chocolates. However I think the best way to surprise you lucky lady is listen to her and be creative. Make sure its something she wants or wants to do, so needless to say you gotta hear past the blah blah at times. To be able to see the hints females will throw at you however suttle they may be.
Then, of course it comes down to tastes, what she likes best. A nice dinner you have made yourself, served in a clean, tidy home you took care of :-). Or a a cute poem about her (not necessarily sugary... funny could do it as well), written by hand in a piece of white paper which is wrapped around a rose. How does that sound :-). Went too far..lol?