Well since you are asking about cereal, infant rice cereal is a pretty popular option. Easy to digest and all. Infant oatmeal would be another cereal option. Then some people skip cereal altogether and go with popular first fruits or veggies like avocado, banana, carrot, squash.
You can also make your own rice cereal if you choose to go that route. We started with Sweet Potato about a week ago and are now doing Butternut Squash. We never saw a point to the rice cereal.
Re: Introducing baby cereal
https://wholesomebabyfood.momtastic.com
is a great resource on baby foods in general. Tons of info there. Highly recommend you look there for info.