Haven't you ever heard her mention something in passing? Women give men all types of hints if men would just pay a little attention. She might see something in the store and say "Oh, thats nice" etc.
How about a gift certificate to Victorias Secret? Or are there any couple'* retreats around? I had this one guy take me to a place like that and it cost $500 for one night but it was well worth it. There was a 20 ft swimming pool in our room, a sauna, jacuzzi, mirrored ceiling. It was unforgetable