Even though cats are the rabbit's natural enemy and a predator of this prey animal, both rabbits and cats have similar body language and can become great friends.
Below is an excerpt from Living with a House Rabbit, by Linda Dykes and Helen Flack. I highly recommend you buy the book, it has helped me a lot with my house rabbit when I first got her!
One factor that facilitates cat/rabbit friendships is the complementary body language of the two species. A dominant rabbit may push his head under the cat's chin, "presenting" in order to demand a lick. With cats, it is the dominant one doing the grooming so, when a cat grooms a rabbit, each animal happily believes he is the boss!
The best strategy is you want a house rabbit and cat to live alongside each other is to choose a large bunny (or small cat...). You need to be cautious if your rabbit is a dwarf breed and your cat is a hunter.
The rabbit and cat should have separate litter boxes.
Step 1: Take the rabbit into a room with a door that closes and locks. If at all possible, keep the other pets away from the rabbit, only allowing them to smell it from behind the door.
Step 2: Allow the cat/dog to see and smell the rabbit, but provide a way for the rabbit to escape if it feels threatened. Don't allow the cat or dog to be able to touch the rabbit.
Step 3: Introduce the rabbit to a single animal family member at a time, in a small area where they can smell, see and touch each other. Supervise the entire time, and remove the rabbit immediately if any aggression or hostility is shown by either animals.
These 3 steps should take a while to get through. The actual time will depend based on your animals, how many you have, and how frightened the rabbit is of them. Each step might need to be repeated several times. It could take anywhere from a couple days to a month, or much, much longer. Definitely don't rush the process; and never force your animals to become friends. It must be their decision.