Ok, I've got a Canon EOS 450D. (Rebel XSi). I currently have the lens that came with it, (18-55mm IS), a 55-250mm IS and the 50mm f1.8 Lens. My wife told me I can have one new item for my camera this Christmas. I was contemplating if I should pick up a flash, like the 430ex ii, (not the 580 ex because its too expensive). Or a new lens. For the lens I want one that's got pretty good light sensitivity, (somewhat like the 50mm f1.8) But I want to be able to have some kind of zoom capability too. What should I get?