I would check out this thread!
http://www.ratshackforum.com/forum/showthread.php?t=32047&page=1
It's pretty lengthy, but there's a lot of good conversation about what's good for rats, what they need in their diets, how to make your own mix, etc.
However, KatTheHippie listed all the fruit and veggies she gives her ratties later in the thread so I'll save you some time!
"bell pepper (red, green, orange, and/or yellow. I usually grab a few of each and switch it up) blueberries, raspberries, blackberries, strawberries, pomegranate, cantaloupe, honeydew, apple, pear, peach, plum, carrot, tomato, broccoli, cauliflower, celery, cucumber, greenbeans, peas, spinach, kale, dandelion leaves, mint, watercress, parsley, basil, cilantro, carrot tops, beet greens, swiss chard, collard greens, arugula, green leaf and red leaf lettuce, and romaine"