I've seen alot of talk over on Backyardchickens about the proper diet for domestic rabbits. I cannot say for everyone that what I do is the best, but I have extremely healthy rabbits and have never lost one yet to anything.
Tha vast majority of rabbit fanciers and breeders agree that the main staple of the diet should be hay so we will start there.
Hay:
Most rabbits benefit greatly from having free choice hay. It's not rocket science either, Orchard or Meadow grass or Timothy hay for adults and Alfalfa for babies and nursing does. Free choice, meaning toss in a handful in the morning and when that's gone add some more, or use a wire hay rack, etc. Just always have hay available.
Just like humans need 6-8 glasses of water a day, I feel that all rabbits need hay. They need it for roughage for their digestive system and to keep their teeth well ground down. Chewing hay also reduced stress in rabbits and they tend to sit and chew hay and have large amounts of bowl movements at the same time, the act of eating hay is just good for them overall.
I have heard the argument of "Well my rabbit doesn't like hay and won't touch it". To this I can only say "Try harder" Your rabbit is probably getting completely full on the amount of pellets you are offering and therefore doesn't want the hay. Reduce the amount of pellets drastically for a few days or offer hay and then feed pellets a few hours later. I bet you'll start to see little cottontail turning over a new leaf!
You can also trying making it fun! Stuff some into an emtpy toilet paper tube, put some into a plain brown cardboard box with no labels or anything on it, add some applewood sticks for chewing and let bunny have a blast opening his own present! The possibilities are endless!
Also another tip! DO NOT buy those teeny bags of Timothy hay from the petstore. They are usually VERY stale (think years in some cases) and you are being RIPPED OFF price wise! Some of those small bags can cost $10+ when you can buy an entire bale of hay for less than that at the feed store! What if I only have one or two rabbits? Won't I waste all that hay?! Nope. When I only had one rabbit two years ago, I would buy an entire bale and it would only last me 5-6 months. Stored well and kept dry and free of yuck it will be just as fresh in 6 months as it was when you bought it. I kept mine split up in big rubbermaid tubs with lids inside my garage. Worked perfectly.
Pellets-
Feeding pellets is important. Feeding high quality pellets without junk is even moreso.
These Rabbit Diet concoctions from Wal-Mart and the major chain petstores are GARBAGE! If you're rabbit food has colorful pieces of "fruits" and "veggies" and dyed bird seeds, you really need to throw that junk out and go buy soemthing better... All of that stuff is un-needed and like feeding them candy all day long.
You want to look for a Timothy based pellet. Yes, your rabbit pellets are made based on pulverized hay, or let me say they SHOULD be anyway!
I love the Blueseal Brand personally and I feed Show Hutch Deluxe by them. One of the reasons I love it is that it contains Papaya and I have Angora rabbits. Papaya is known to help prevent wool block in rabbits.
A quality rabbit feed should be high in fiber, 18% min.
Water-
Might seem kinda dumb to have to write this but fresh water should always be available. I have found that the pin style water bottles are tough on rabbit teeth and that senior rabbits tend to enjoy drinking out of a bowl over a bottle. I bleach out my water bottles and bowls once a month.
Veggies, Treats, Supplments-
Supplements:
You can buy a variety of nutritional supplements for your rabbits. Again, I like Blueseal Sunshine Plus. But there is Show Bloom, and Doc Rabbit something or other, and many more... Mostly these are used by show people to bring on the "bloom" of a showing rabbit, meaning to put them in top condition for showing and breeding.
Veggies-
There are a ton of different acceptable veggies to give as treats to rabbits. The key is to use sparingly. You can "kill them with kindness" essentially.
Treats-
Most of the commercial rabbit treats on the petstore market are junk, like going out and buying a bag of cheetoes for yourself. I imagine a little now and then wouldn't hurt but don't overdo it!
I found your post really helpful though.... 
