Crush the Castle is an action flash game developed by Armor games. The goal of the game is to kill all inhabitants of various castles by using a trebuchet to fling large rocks or bombs at them.
The same game is redesigned as Angry Birds.
There are many ripoffs of angry birds too
check here http://www.pocketgamer.co.uk/r/iPhone/Angry+Birds/feature.asp?c=39088