In 4- to 5-quart slow cooker, combine black beans, kidney beans, garbanzo beans, onion, red and green sweet peppers, chili powder, garlic, chipotle chile pepper, cumin, and salt. Add tomatoes and broth.
Cover and cook on low-heat setting for 8 to 10 hours or on high-heat setting for 4 to 5 hours. Stir in cilantro. If desired, serve bean mixture with rice.