Rose Elliot has a really great one in an older edition of her New Vegetarian Cooking. This she had on her website. http://www.roseelliot.com/catalogue_item.php?catID=2032&prodID=10993 The cookbook version uses canned tomatoes as the base and a larger variety of vegetables, but it is simple.

I love this recipe--which is more like a method--and I've executed it with all sorts of vegetables like roasted red pepper and zucchinis
http://www.barefootcontessa.com/recipes.aspx?RecipeID=234&S=0

My recipe for Ribollita is a simple version of Tuscan vegetable soup thickened with bread and flavored with tomato, kale, potato, and beans. It's hearty and warming on a chilly day.
http://food52.com/recipes/14464_ribollita

Here are two of our favorites -- both very simple:
http://food52.com/recipes/9743_roasted_carrot_soup
http://food52.com/recipes/15247_paul_bertollis_cauliflower_soup