Check the Library Veggies thread for lists of safe foods:
http://www.rabbitsonline.net/view_topic.php?id=13618&forum_id=17
My "poor" rabbits have less variety right now because the garden is dead for the season. I grow a lot of veggies for them, including a bunch of different herbs that I can't get in decent amounts in grocery stores. Even with having to rely on grocery stores I change it up a bit so they aren't getting the same exact thing all the time. Right now they are getting red leaf lettuce, escarole, parsley, collard greens, turnip leaves, canned pumpkin, and the occasional bit of cauliflower.
Other grocery store veggies I often get- any kind of dark, leafy lettuce, any kind of cabbage but purple is their favorite, kale, cilantro, dill, mustard greens, swiss chard, bok choy, spinach, carrot greens, carrots, broccoli, alfalfa sprouts, and pea pods.
I make sure to feed a lot of variety, because as far as Fey's concerned the less pellets and the more veggies she gets, the better. Of course, it's easier to have a variety when you have a lot of rabbits to eat it all up! When I just had Mocha I would buy lettuce mixes, especially Spring Mix, and some herbs and that was about it. If I bought much more, most of it would have gone bad before she could eat it all.
I do feed the veggies reputed to be gassy, such as cabbage, broccoli, and cauliflower, because none of my buns have problems with them. I'm not feeding them to the foster bun Luna yet since veggies are still new to her. She already went from zero veggies to a big handful twice a day in about a few days stretch because veggies were about all she could eat due to molar spurs. She was fine.
Edit: Normally when adding something new, give a small amount for a few days and stop if the bun seems to have issues such as gas, runny cecals (messy butt), etc. Some rabbits really are sensitive, just not mine. Of course, every single rabbit in this house would sooner bite me than eat banana, so they can all be a bit different.
