Yogurt wins by a nose over low-fat milk. An 8-ounce cup of plain yogurt will give you about a third of your daily needs. The amount of calcium can vary, so check labels to be sure you're getting enough.
Orange juice and milk made from almonds, rice, and soy that have the nutrient added to them are also good sources. Shake the container before your pour though, because the calcium can settle to the bottom.