100% approved by our army of gals and our field report earns us a few bucks.
Focus on the message. If you don't take some time to fill out the card, then this is nothing more than a chocolate bar. Write a few sentences to tell her how you feel about her. You don't need to write a poem or anything like that. Just be real and put down something nice.
These make for good surprises. Try leaving one of these in a place where she'll come across it on her own...maybe in her purse or under her pillow. The implied message here is that you often think about her when she's not with you. Gals dig that.