I currently have the following equipment and am looking to make my next purchase. Canon XT Camera Canon EF 28-105mm f/3.5-4.5 II USM Canon EF 50mm f/1.8 II Most of my photos are of my kids and are action photos on a football field. One of my daughters is a cheerleader, one is on drill team and my son plays football. Some of the games are day games and some are night games and most of the pictures are taken from the lower section of the stands. I have a budget of about $400 -$500 and am not sure if I should buy a flash or a lens or both for my next purchase. My thoughts are to buy a Canon 430ex flash and a Sigma 75-300 APO or Canon 75-300 lens, but am not sure if there is a better choice. I would appreciate your advice!