K.W.
Vegetable soup with beef stock.
And once you've cooked the bones, the bone marrow is a delicious treat. As a kid, my mom would scoop out the marrow, spread it on a piece of white bread, and salt it. Since there were 4 kids, she'd have to cut the bread into four pieces so we'd each get one. (I'm guessing that there was a second piece of bread with spread that she enjoyed all to herself.) Delicious! This may be one you have to grow up eating to enjoy, but I recommend it if you're adventurous.
(Bone marrow seems to be the trend item in Portland, OR restaurants these days.)