Have you taken lots of images of the two of you together? There are some great programs (Real Media used to offer one called Slideshow) that will let you blend scanned or digitial pictures with a song (it'll convert your favorite MP3) and fade pictures in and out at a speed of your choosing. I gave one to a girlfriend once and she absolutely melted.
If you go with flowers, I'd suggest something other than roses. They're too predictable. Try sunflowers or tulips or some other type your GF likes. Shows that you're paying attention and not just following protocol.
Of course, there's always jewelry, too.
