When you bought your digital camera a couple of years ago, it was a marvel of engineering. Then the next generation came out. And the next. Now your revolutionary camera feels more like an antique. But with so many choices on the shelves, how do you choose the right replacement? The trick to finding your perfect match is knowing which features are most important to you before you step foot in the store. Derrick Story explains how to figure out what you need in our digital-camera shopping guide.