From what I know you should never give them lettuce, only dark green salads. Any herbs are good (my bunny loves basil and carrot tops), but avoid too much parsley as from what I heard it is very high in calcium.
Also ,I know I don't give my bun any veggies that might cause gas as they end up at the vet;s and it can be very painful (I'd rather not tempt it), so all greens like cabbage, sprouts, peppers... etc are out...