There's nothing like homemade stock. There are good commercial stocks out there, and I use them, but they never are as rich and flavorful as the stock I make myself.
I have spoken before about thrift in cooking. I save old bread , and find recipes for radish and carrot greens I would otherwise throw away. For my stock, I save the vegetable trimmings, rib bones, poultry carcasses, and ham bones.
Whenever I work with vegetables, I save the trimmings in a sealable bag in the freezer. Potato, carrot, turnip, and parsnip peels are obvious. The outer layers from onions, as well as the fibrous part of leeks and green onions adds much flavor. The ends trimmed off of celery, and whole stalks when they go rubbery, go into the bag. The woody ends of mushroom and asparagus stems are particularly good for adding richness to a stock. I like to include bell pepper trimmings as well.