When I was younger, I used to love to listen to my chickens' noises and try to imitate their sounds. They do have a pretty interesting language all their own, and it isn't too hard for people to figure out what the different noises mean if they observe their chickens' behavior.
There are a couple chicken calls that are pretty easy for people to do. The rooster's "I found food!" call is one of them (I think it sounds like, "Tk tk tk tk tk!"). Try to do it at the same rate of speed the rooster does. My big white rooster would go on forever making the "Tk tk tk tk!" noise, and the hens would come running. It was like he was so excited about his meal that he forgot to start eating it. He'd be clucking as he was stuffing his face, too.
Another call that will get your chickens freaking out is the sort of cackling noise of alarm. They start off with a sort of low, "Buck buck buck buck...," speed it up a little, and then go off with a loud, "Be-gawk!" ("Buck buck buck buck buckbuckbuckbuckbuck be-gawk! buck buck be-gawk!")
If you have any flighty or paranoid members of your flock, this will really get them going.
There are a few more sort of clucking, growling sounds you can learn to do, but they are more in the back of the throat and are hard to describe with the Roman alphabet. Hee hee... Just listen to your chickens and try to imitate them closely. You'll get a few odd looks from family members, but it's pretty fun to attempt to communicate with your animals in their own language.