One of the smaller & lighter x-bows out there is the Barnett RC-150. My buddy bought one for his son many years ago and he used it well. It is the smallest, lightest x-bow I have ever handled while still having enough power for hunting. It is also the quietest x-bow I have ever shot. They have taken several nice deer over the years with it.

He put a red dot scope on it, and it is deadly out to 20 - 25 yards.