I cook almost everything in cast iron- I've got 4 pieces of cast iron cookware:
A shallow skillet - great for potatoes, pan-fried fish, making quesadillas
A deeper skillet - great for larger quantities, chilli, stir fries
An un-enameled dutch oven- great for stews, chilli, beans, making sauces, deep frying
An enameled dutch oven - big enough for a whole chicken, great for bigger stews and stuff
Besides my crockpot, grill, and a stockpot, these are pretty much the only pieces of cookware I use. They will last forever, they get better the more you use them, and they can be used anywhere: stovetop, oven, grill- I even used them directly on the campfire during camping a few weeks back.
I like them because they're versatile, old school, no-nonsense (none of that non-stick coating BS), and they heat so nicely.