I made a watermelon salad on Sunday. Actually, I made 3. The first one I made had a yogurt dressing. I felt the yogurt didn't add much so I nixed that. The second one (the one pictured) had a red wine vinegarette, Parmesan cheese, and ground cashews.
I made one in the even for a dinner party I was hosting and that one had only lime juice, salt, red onions, and yellow peppers.
The general consensus seems to be that the lime juice and salt was the most refreshing of the 3 dressings and it really brought out the flavor of the watermelon instead of simply masking it.