There is a product called Ropel that you can spray on the foliage. Won't harm the plant, but makes the leaves very bitter and the bunnies won't continue to munch. It is a bit pricey though, and needs to be reapplied after rain.
I've also used red pepper sprinkled on the plants, a cheaper alternative. It still needs to be reapplied, but doesn't cost as much.
Make sure you hit the flowers with Miracle Grow regularly to get them established quickly. Once they reach a good size, the nibbles by the rabbits shouldn't matter.
I also try to use only plants they generally won't eat...impatiens and begonias are two they will leave alone. Some say marigolds, but I've found that if hungry enough they will eat them.
Its gotten to the point in my yard where I plant a patch of 'sacrificial' flowers in the area they love most. They eat there, and leave the other stuff alone.
