One ingredient that is popular to grow are hops. They come from a rhizome, which is basically just a root cutting. There are a few site sponsors that have some deals going on at the moment. nikobrew.com is one, http://farmhousebrewingsupply.com/
and arrowheadhops.com are a couple of others. I've only grown hops for two seasons but they have done pretty well. If you check out the hops growing sub forum on this site there is a lot of good information to get you going. I've read some posts of a couple of people growing barley but I'm not sure how much success was had. If you plan to use spices or herbs in your beers you can grow them as well.