I usually "cheat" when I make veggie soup and start with frozen mixed soup veggies. I usually cook them in watered down tomato sauce (a 1:1 ratio until I have the volume of fluid I need) and then add in a pound or a pound and a half of cooked ground beef.
I once had a mixed vegetable soup that seemed to be based on summer squash or some green gourd, and carrot. Maybe some shredded cabbage. The best thing about it was the texture because every single ingredient was grated! And parboiled, so it was colorful and not overcooked. It was like a party in my mouth. I wonder if it was all parboiled in some sort of stock, too...
Potato soup, of course, is great for windy weather. Sticks to your insides, and all.
If you don't mind there being a meat stock in it as a base, one of my favorite ways to make a vegetable soup, such as pasta fagioli, is to start with some Swanson chicken stock (a full box of it) along with about half a jar of Barilla brand marinara sauce. You can add more of either depending on how brothy or tomato-y you like it. If you don't have any marinara, a tablespoon or two of tomato paste works good too.
I can never seem to find a vegetable stock that I like. The closest would be Whole Foods own 365 brand veggie stock, but even that one I'm not crazy about, it's merely tolerable. Some of them taste like burnt tomatoes in water, while others taste like muddy water, and worse yet, others load them up with salt and MSG to make up for the lack of meat.
For "veggies", since the marinara already has tomato chunks in it, I don't bother with more tomato. I will add a variety of beans, such as Cannelini, Dark Red Kidney beans, chopped fresh or frozen green beans & wax beans, or maybe even some Chick Peas. For the veggies, I will toss in stuff like Zucchini, Yellow Squash, diced Potatoes, Spinach or other greens. Occasionally corn and peppers too.
I almost forgot to add, Carrots, Celery and Onion - but I put those in practically every soup.
In the summer, there's no good reason at all not to grill the vegetables for your soups, unless you just don't like the taste of grilled vegetables. I made a minestrone a couple of weeks ago with grilled vegetables (asparagus, onions, tomatoes, and zucchini), along with white beans, seashell pasta, vegetable broth, and Italian seasonings. It was almost too intense on the grilled flavor, but it was really good.