Water-color stripes! Basically, you just use water color stuff and paint stripes across the cover of your card. :)
Chalk paint! Using chalk paint, paint a heart on the cover of your card. Then you can write something (with chalk) on it once it dries. Just thought that was cool... :)
FEATHERS! This one is probably my favorite. :) Get some paint and make a feather shape on the cover. Once it dries, get an inky pen and fill in all the feather details. :) Coolio.
Which one's your favorite?