A Dutch Oven.
In the winter months, I use mine constantly. I have two, both made by Le Crueset. One, I inherited from my grandmother & the other was a gift from my MIL. These pots can be very expensive, so I'm happy about that. I know that there are many less expensive versions, that supposedly work very well. Try someplace like Target...I hear they sell some that are very highly rated.
Dutch oven's are perfect for making stews, soups, tomato sauce & any kind of braising.