if you want a great tennis workout, Bruce Nagel Tennis Academy has exer-tennis classes for adults that are the bomb! Talk about fun and heart pumping! It is head and shoulders above any USTA cardio-tennis or similar workout that I've been in and I've been in alot both in Hawaii and on the mainland. Some of the students have been in it for 20 years because it is such a fulfilling workout. I can see myself doing this forever--FUN, FUN, FUN! and great for tuning up your game for league too. The Kailua Racquet Club is also really pretty and everyone is friendly and welcoming.
Pros: Professional and knowledgeable staff, beautiful setting, great value
Cons: a little far from Honolulu--about 30 minutes