I love tortilla soup but every time I make it I find it lacking.  For this reason I have never made it the same way twice, always trying to find my perfect recipe.  Well, I think I've come close at last. This is an adaptation from Jen and Lauren's recipes with a chicken marinade I found that I think is what makes the soup.  
Tortilla Soup
3-4 boneless, skinless chicken breasts, cut into cubes or strips
Chicken Marinade:
1/4 cup olive oil
1 tsp lime juice
2 tsp Worcestershire
1 1/2 tsp cumin
1 tsp salt
1/4 cup chopped cilantro
1/2 tsp oregano
1/2 tp pepper
2 cloves garlic, minced
1 can beef broth (14 1/4 oz)
1 tsp chili powder
In a medium bowl, mix all ingredients together.  Add chicken and mix well to coat all pieces. Cover and refrigerate for at least 1 hour or overnight.  
Soup:
I garlic clove, minced
1 onion, chopped
1 Tbsp margarine
2 14 1/2 oz cans chopped or stewed tomatoes
2 14 1/2 oz cans chicken broth
1 cup salsa (we use Pace chunky, a 16oz jar will be about a cups worth)
1Tbsp ground cumin1 can black beans
2 tbs, seeded and chopped jalapeno (Lauren's recipe calls fr this but I never use it since I like my soup more mild)
In a crockpot  melt margarine and add onions and garlic.  Saute until onions are tender.  Or saute them in a pan and pour them into the crockpot when tender.  Combine all ingredients in crockpot and add all contents of marinade and chicken.  Stir to mix.  Cover and cook on low 8-10 hours or on high 4-6 hours.  
Toppings: 
tortilla chips
sour cream
shredded cheese
diced avocado
To serve put chips on bottom of bowl and ladle soup over top.  Add cheese, a dollop of sour cream and avocado on top. Mmmmm.