1. Romantic Date
Eventhough you've been with her for years but I think it'd be nice if you do it again like when you do it on the first time you fell for her. Trust me She'd love this idea a lot. You may ask Her for diner on a restaurant with a beautiful view. Diner on beach maybe,watching the stars together.It'd be very romantic for Her. Or you may ask Her to go to the place when you spent your first date together.
2. Special Vacation
I reaaallllyyy deeply suggest you to use this idea. Spent some days with your girlfriend at a special place just two of you. It may be a second honeymoon for you who have already married. Hmm if I were your girlfriend I'd be really love if you ask me take a vacation on cruise. I know that's sooo expensive.But it's worthed.Hehehehe. Just ask Her on a special and romantic place that would never be forgetten by to of you. So when you two get back from your vacation, She will happily tell about Her most wonderful vacation with you _n n_
3. Make A "Special Surprise Moment"
This is the hardest one. But I guarantee it's 100% worthed to try. You really need to use your imagination on this one.For example, you may spread lots of rose petals around Her house or apartment make it like you're making a special road for Her.Then on Her front door,stick a picture about you and Her that special most. Don't forget to decor it with flowers or others.Then after that,when your girlfriend find it and follow your 'road' to Her front door. She will be more surprise with what you did on it then it'd be a perfect moment to hug Her from behind and then wishper that you love Her. You may use other idea on this one. Just use your creativity.