During the Victorian Era each flower had a different meaning. Red Roses are the traditional Valentines day gifts because they signify true love. Other colors mean other things: white means purity, and yellow is friendship.
One way to chose a different flower is to look for one with a meaning which fits your relationship. Red Chrysanthemums, forget-me-nots and myrtle also signify love. Monkshood and yellow daffodils signify chivalry. Clematis is a complement to one's intellect, fennel means praise worthy, and hibiscus means delicate beauty. Giving anything requires thoughtfulness, so try to think of what flower she would like to get. Think back to the flowers that were around you when you hiked through the woods, when you got married or when you went on your first date. A bouquet of these flowers with a thoughtful note would be a wonderful surprise.
Most people have a favorite flower which provides a safe fall-back. And I hear that everyone loves tulips. Almost any kind will work it depends on what the person likes. you should really get that special girl some orchids mixed with carnations and if you want and different colors of roses to really make it special. Roses are probably the best flower though but its the thought that counts! The carnation seems to be forgoten in this... the carnation is as far as I know the second most given flower on valentines day. If you're looking to give a friend a flower a white carnation is good for that.