2 cups black beans, drained and rinsed
3/4 cup sour cream
3/4 cup salsa
Lime juice to taste
Guacamole
Grated cheddar cheese
Shredded lettuce
8 taco shells

In the food processor, combine the beans, sour cream, and salsa. Puree until smooth and transfer to a bowl and mix in lime juice to taste.
Put out remaining ingredients in bowls and let diners assemble their own tacos.