The following are some common flowers that are edible. If you ever find yourself locked in the botanical garden after hours, you might make a salad of these:
Carnations – Petals are sweet.
Crysanthemums – Petals are tangy and slightly bitter. Leaves are allegedly edible as well.
Clover – Tastes like licorice.
Dandelions – Petals taste like honey when picked young.
Roses – All roses are edible. The darker flowers have the most pronounced flavor.
For a longer, more detailed list, check out this site.