I've recently been given the opportunity to expand/upgrade my equipment. I currently use a Digital Rebel XT and shoot in natural light. That said, I have the ability to either purchase a new camera (40d), a new kick ass lens, or a lighting kit (power pack, umbrella soft box, etc.). I shoot concerts and headshots/portraits. Now, my question to you all is: Which of the three items listed will help me the most? If you could only buy one, which would it be?