I'm finally ready (financially) to get a new lens for my XSi. (That's 450D for you internationals.) I'm wondering what makes the most sense to buy, given I can only afford one lens. So far I've been looking at these options: 50mm F1.4 Something Similar to the kit lens, just better (17-80mm?) Ultra Wide Angle (9 to 10mm at it's smallest) So what are the best options for these types of lenses? My limit is around $350.