Offer a variety of vegetables daily. Just like for humans, these veggies are important in order to obtain the necessary nutrients, with one each day that contains Vitamin A, indicated by an *. Add one vegetable to the diet at a time, especially if your bun is not used to eating vegetables. Eliminate if it causes soft stools or diarrhea. 

Alfalfa, radish & clover sprouts
Basil
Beet greens (tops)*
Bok choy
Broccoli (mostly leaves/stems)*
Brussels sprouts
Carrot & carrot tops*
Celery
Cilantro
Clover
Collard greens*
Dandelion greens and flowers (Be very careful about pesticides)*
Endive*
Escarole
Green peppers
Kale (!)*
Mint
Mustard greens*
Parsley*
Pea pods (the flat edible kind, snow peas)*
Peppermint leaves
Raddichio
Radish tops
Raspberry leaves
Romaine and Red Leaf  lettuces (no iceberg or light colored leaf)*
Spinach (!)*
Watercress*
Wheat grass

(!)=Use sparingly. High in either oxalates or goitrogens and may be toxic in accumulated quantities over a period of time

You may also add fresh fruit to your rabbit's diet. Fruits should be used only sparingly, as occasional treats. Bunnies have a sweet tooth and if left to their own devices will devour sugary foods to the exclusion of healthful ones.  Try:

Apple (remove stem and seeds--the seeds are poisonous)
Blueberries
Melon
Orange (including peel)
Fresh Papaya
Peach
Pear
Pineapple
Plums
Raspberries
Strawberries

Bananas

Grapes

Raisins or non-sugar-added dried fruits (usually available in health food stores)