Did you know that those little boxes of vegetable stock at the supermarket are, like, $3 each? Or more? So that every time you want to make a pot of soup, someone is getting $6 of your hard-earned cash! And those stocks in a box or can DON'T EVEN TASTE GOOD! I suggest that you declare your freedom from nasty stock in a box. All you need is a freezer, a plastic bag or large container, a pot, water, and some herbs that you probably already have lying around anyway.
Here's what you need to do: Whenever you are chopping vegetables, save the scraps. I particularly try to save the scraps from onions, carrots and celery, as that will form the base of your stock. Save the skins from the onions, too, as they lend a nice golden color, like Grandma's chicken soup. You also want to save your parsley stems, as well as the scraps from any of the following "stock-friendly" veggies: tomatoes, mushroom stems, zucchini, red or yellow bell peppers (no green! yuck!), leeks, potato peels. Avoid the cruciferous vegetables - cabbage, broccoli, cauliflower and the like - as well as asparagus, as they will lend a dominant and somewhat unpleasant flavor.
When your scrap bag is full, and you are doing other stuff around the house for a few hours, it's time to make stock. Aim for a ratio of one part onions, one part carrots and celery, and one part "other stuff". I usually throw in a fresh onion, as well as some fresh carrot and celery. I also like to add a splash of tamari, a bay leaf, a few branches of thyme, and a few peppercorns. If I have dried mushrooms in the house, either porcini or shiitake, I will include a small handful of those as well.
Now add your veggies to your biggest soup pot, fill it with water, bring to a boil, and then reduce to a simmer. At this point you can go do other stuff. Unlike animal-based stocks, you don't need to worry about standing around skimming it all day, as there won't be any impurities to remove. Your stock is done when you say it's done, usually after about three or four hours of simmering at a very low flame.
I like to cool the entire pot in a sink full of ice water, and then let the whole thing sit in the fridge overnight before straining. This is partly because I am lazy, and partly because I think it develops nice flavor that way. Once you've strained your cooled stock, pack it into freezer-safe quart-sized containers (such as glass jars -don't forget to leave an inch of head space at the top of the jar to prevent cracked glass and ruined stock!), and freeze what you won't be using within the next four days.
Voila - instant stock, nearly free, and you get to stick it to The Man when you stop buying all those $3 boxes of the nasty stuff.