For the fresh salsa, shuck the corn cobs and cut off corn kernels. Place the corn on a baking sheet in a single layer and broil 5 minutes until tender and bright yellow.
Dice the tomatoes. Drain and rinse the black beans very well by placing them in a bowl with water, then thoroughly draining (this step is important to avoid incorporating the can juice, and is not necessary for cooked beans). Chop the cilantro. Juice 2 limes.
In a medium bowl, mix together corn, tomatoes, black beans, cilantro, lime juice, cumin, and kosher salt. Stir to combine; taste and adjust additional seasonings as desired.