just got my xti and starting to shoot everything already, I found that my lense that came with the kit 18-55mm f3.5-5.6 is very restricting especially indoor shots. I want to purchase 2more lenses for to meet all my needs and in need of some advice. My next purchse will be 50mm f1.8lense and I need a third lense for some portraits or upclose pictures what do you guys suggest? sigma 55-200m f4-5.6 is $139 at adorama. Are these 3 lense ok for just about anything? or am I missing something?