Normally I will feed my chickens this chicken starter feed,
It's just little round pellets, it has vitamins, protein, calcium and fiber in it. There is also feed that comes in mash, and crumbles. Around July I will move them off the chicken starter feed and on to layer feed to give them the nutrients they need to lay eggs. I found this chart off of IFA's website Poultry Feeding Chart it shows you how long your are suppose to keep the birds on a certain type of feed and when to change to a different type depending on what type of bird you are raising. I found some useful information at the IFA website, it also talks about how to take care of the birds you should check it out if you are interested to learn more.
In addition to the chicken feed I have also fed my chickens worms (they weren't to sure what to do with them at first, my Dad has fed them carrots, and yesterday we fed them watermelon and leftover corn on the cob. They didn't show much interest in the corn but they loved the watermelon.