Cook onion, garlic, cumin and pepper flakes in oil in 4-quart saucepot over medium heat for 3 minutes or until onion is tender. Remove from heat.
Place 1 can beans (with liquid) in blender, add ½ the broth. Cover, and blend until puréed. Stir into saucepot. Repeat with one more can of beans and broth. Stir in remaining can of beans (whole), salsa, and lime juice.
Heat mixture to boil. Reduce heat to low and stir in chopped cilantro. Simmer 30 minutes.
Ladle soup into each bowl; top with dollop of sour cream. Garnish with broken tortilla chips and snipped cilantro.