Unleash your inner rock star with Pound. This "cardio jam session" utilizes weighted drumstick-like Ripstix while participants drum to the beat. The squats, lunges and other ab-heavy moves are especially good for anyone who wants to work on their core fitness, but the party atmosphere is even better for forgetting you're actually exercising. Classes have spread nationwide; find one in your area here.
Chances are you've seen Bosu balls at your local gym: They look like someone took a balance ball and chopped it in half. What you might not know is how versatile Bosu balls can be when it comes to exercise: Ball side up or flat side up, they can add a new level of difficulty to standard moves since you must work to stay balanced. Even better, you can get a great Bosu workout on your own (but if you're a social butterfly, some gyms and rec centers have Bosu-centric classes or incorporate Bosu balls into other classes).