This might be the absolute best gift you could get a tennis nut right now. The Dynaflex Power Ball is the single most purchased item from the Upabreak.com site. It's a gyroscopic wrist-exerciser with blue LEDs that glow the more you spin it. It gives you a high-intensity workout for your wrists and forearm. This is also great rehab tool for tennis wrist and arm injuries, and I even use it to warm up a bit if I'm pressed for time before a match.