1. Prepare grill.
2. Soak corn in a large bowl of cold water for 20 minutes. Remove and pat dry. Coat corn on all sides with cooking spray, and season with 1/4 teaspoon salt and 1/4 teaspoon pepper. Grill about 15 minutes or until charred on all sides. Remove cobs from grill, and cool slightly. Slice the kernels from the cobs, and transfer to a medium bowl. Add tomatoes, olive oil, vinegar, and sliced basil; season with 1/4 teaspoon salt and 1/4 teaspoon pepper. Let the relish sit at room temperature for 15 minutes before serving.
3. Meanwhile, lightly coat both sides of salmon fillets with cooking spray; season with remaining 1/4 teaspoon salt and 1/4 teaspoon pepper. Place fillets skin side down, and grill 3–4 minutes or until golden brown. Flip fillets, and grill for 3 more minutes. Fish should feel slightly firm in the center and will register 145° on an instant-read thermometer. Place salmon onto each of 4 plates, and spoon relish over top. Garnish with basil sprigs, if desired.