A rabbit's diet should be made up of fresh green, good quality pellets, fresh hay (timothy, broe, oat hay, or orchard grass), water, and fresh vegetables. Anything beyond that is "treat" and should be given in limited quantities. This includes carrots!
Below is information regarding different diets bunnies require at different stages of their life as well as some websites and other resources for ordering hay and pellets.
Babies (Birth-7 months)
Young Adults (7 months-1 year)
Mature Adults (1-5 years)
Seniors (Over 6 years)