Here is a good diet summary that refers to the House Rabbit Society as well.
It explains the importance of hay too. As Watermelons explained, hay is the most important thing to feed a rabbit to prevent GI stasis. It should be unlimited and available 24/7. A few pieces isn't near enough. A rabbit should actually be eating about its body size in hay every day!
Just know that they tend to be choosy about which pieces of hay they eat. They like to pick through a quantity of hay. They also eat more hay when it is refreshed, so adding more hay daily is important.
Cannot stress enough the importance of hay, lots of hay, every day -- the best way to keep a rabbit's gut healthy.