Here's a pitch for functional training, which I discovered about 14 months ago when I joined a fitness studio near my home. It's a full-body workout that engages that all-important core, using movements that mimic things you actually do on a daily basis (bending, squatting, lifting, reaching, etc.) and utilizing simple equipment such as balance balls, medicine balls, stretchy bands and free weights.
At my studio, the workout consists of two full rounds of 15 "stations" of 45 seconds each, with exercises that change every day, and give you the full complement of strength training, aerobics, stretching and balance/coordination. I do this three times a week, and do other activities (running/walking, biking, kayaking, etc.) on other days.
I knew I was sold on functional training last summer, after having been a member only a month, when I went on vacation and blazed up steep hiking trails with little of the aches (knees, back, etc.) and breathlessness that used to plague me in my younger, "healthier" days.
It doesn't take much effort to incorporate functional training into your lifestyle; I even manage to do a challenging workout when I travel. I recommend it highly! To get you started, here's a good video with examples of a few core exercises. Happy training!