If it's tomato soup, I serve it with grilled cheese. Chili or soups with lots of beans get served with homemade corn bread (corn + beans = a complete protein). We have a local water-wheel powered grist mill that grinds locally grown corn, so any excuse for corn bread is a good one (though you need a fanny-slicer to buy a small bag of corn ... definately not a "frugal" purchase!) The kids come with me to watch the 300 year old waterwheel turn the gigantic millstone to grind our corn, so I consider half the cost to be "entertainment expense." We bake traditional "baking soda" sweet corn bread in the oven.
If I'm serving something Germanic in origin with sausage (hot dogs, keilbasa, bratwurst, gumbo, etc) or Boston baked beans, I like Russian Black Bread, any type of molasses-corn based bread, or Yankee Brown Bread (the kind you steam in an empty coffee can). The molasses in the bread really meshes well with the sausages (just not italian spiced sausages, which prefer a white bread).
Anything else gets a hearty bread machine bread using whatever ingredients I'm in the mood for. We bought a reasonably priced bread machine cookbook with over 100 recipes many years ago and it has earned it's keep. The kids favorite is a semi-sweet apple-oatmeal-raisin yeast bread (made when we have leftover fruity oatmeal from breakfast). Bread machine bread is fine, but in cold weather -if- I get back from after school activities before the machine kicks into the last "bake" cycle, I pull it out, hand knead it one extra time, and pop it in the oven to bake. I realize this uses more energy, but the consistency from that extra step gives the bread the consistency of those fancy bakery artisan breads. And if I don't get home in time or it's too hot outside ... bread machine bread is fine with a hearty homemade soup.