Feeders

There are a number of ways to deliver the feed to the rabbits.  Pellets are usually provided either with J-feeders or crocks.  Hay can be provided with a pellet-hay combination feeder, racks, loose, or even on specially-designed cages.  Some breeders like to provide creep feeders for their litters which keep the mother from eating the specialized feed.

Crocks
Crocks require you to open the cage to feed the rabbit, must have fines dumped from them, and often collect fecal waste.  However, some people still like to use them.  Crocks can be loose or attached to the side of the cage.  If you choose to use loose ones, make sure that they are the kind that cannot be tipped over, or you will be dealing with a lot of wasted feed.  Ones that attach to the cage make it more difficult to dump out the fines and feces, although you can usually mount them high enough that you shouldn't get as much poop in there.

J-Feeders
The biggest advantage of J-feeders is that it can be attached to the outside of the cage, with the trough inside the cage through a cutout, allowing you to feed the rabbits from outside the cage.  Because they are attached to the cage, the rabbit cannot tip them over.  The original J-feeders were made completely out of metal, and did have to be detached from the cage to remove fines.  Most feeders today, though are made with a mesh bottom.  Most have hardware cloth as the bottom, which sifts all of the fines out of the feed as it is poured in. Hardware cloth can be destroyed by digging, though.  For rabbits which dig in their feeder, I recommend getting feeders with diamond mesh.  The downside to diamond mesh is that it can sometimes catch pellets that will have to be poked back through.  J-Feeders are usually sold by how wide they are, in 3", 5", 7", 9", and 11", and some brands will go wider.  3" feeders are really only useful for small breed bucks and replacement breeders.  I suppose some meat breeders do use the 3" feeders, but some bucks can have rather broad heads that can make it difficult to eat from 3" feeders.  I prefer to use 5" feeders for meat breeds, and even giants can get by with 5" feeders, especially if you get the wide-trough type (also recommended for lops).  Litter pens should have at least 7" feeders, whether for small breeds or larger.  That way, there's more room for everyone to eat.  Keep in mind that in addition to the feeder, you will also need to have water access on all of the cages, so wider isn't necessarily better.

Hay Feeders
Combination feeders are great for people who feed hay with their pellets.  Because the front of the feeder isn't there, combination feeders cannot hold as many pellets.  This is really only an issue for litter pen feeders, since most bucks and replacement breeders can still be fed enough feed in the bottom of a 5" feeder.  For litter pens, you will need a wider feeder in order to provide enough pellets for the litter to have a constant supply without you having to add pellets twice a day.

Another option is a hay rack, just holds hay up to the side of the cage and allows rabbits to pull it through the wire.  These can be mounted above pellet feeders for adults, but should be mounted lower for kits to be able to access.

Some people have also designed their cages to have a sloped roof on one side, usually matching up to the sloping side on adjacent cages, which allows the caretaker to simply put hay on top of the cages, and feed several cages at once.

Creep Feeders
Creep feeders are usually long, short troughs with a cover over them that are slid into the cage along one side, and are usually designed so that the trough can be pulled out through the cage wire to be refilled.  The cover has small holes in it just big enough for the kits to eat through, so their dam can't eat it.  You only need these if you plan to feed kits a special diet that their mother doesn't need.