I made a great soup in the crock pot last night, if I do say so myself.  I had beets and carrots in the fridge to use up, but you can use whatever combination of veggies you happen to have on hand.  I think the keys to the flavor are the onions, garlic and spices.

Turkey Vegetable Soup (in the Crock Pot)

Leftovers from the crock pot turkey breast, shredded (I probably wound up with about 4 cups of turkey meat)
2-3 C. beets, chopped into 1″ chunks
2-3 C. carrots, chopped into 1″ chunks
1-2 C. onions, coarsely chopped
2 cloves garlic, minced
2 C. dry lentils
2 cans reduced sodium chicken broth
3 cans water (use chicken broth cans)
1 T. dry tarragon
1 t. Kosher salt
2 t. black pepper

Combine everything in the crock pot and cook on low for 8-10 hours.  Serve with a nice loaf of bread and butter.  This makes a LOT of soup.