I've made almost everything in a toaster oven. Cookies, bread, pie, fries, potato chips, chicken nuggets (frozen and from scratch), cake, roasted Veggies, cassaroles (small ones of course), etc.
if you can find a good model that has a range of features and decent capacity, you're only limited by the size of the dish you're trying to make.
Best thing about it, like catan said, is that it heats up much faster than a regular oven, making temp. control very nice. It's also great to use if you're making a meal with components that require baking but at different temperatures - or to make dessert at the same time as dinner.