Mince garlic and finely chop enough onion to measure 1/2 cup. Cut enough kernels from cob to measure 3/4 cup.
In a small heavy saucepan with a tight fitting lid, bring water to a boil with garlic, onion, cumin, coriander seeds and salt. Stir in rice and cook, covered, over low heat 15 minutes. Stir in corn and cook, covered about 3 minutes or until water is absorbed and rice is just tender. Fluff mixture with a fork and transfer to a large bowl to cool completely.
Rinse and drain black beans. Stir cilantro into rice with beans, lime juice, and salt and pepper to taste.
Serves 4.
See also Cilantro Stuffed Chicken