Milk, Yogurt, cheese, are what most people assume are THE best sources.... but there are many other foods that are just as good!
Some of these include:
Broccoli, Spinach (and most dark greens, for that matter - collard greens, swiss chard, kale, bok choy, mustard greens, etc)..... blackstrap molasses, Sea Vegetables.... Okra... Seed & Nuts (esp. Almonds, Almond Butter, and Sesame)... beans... Lean meats, poultry, fish (esp salmon, & canned sardines) and eggs.