Legs lifts work your ab/adductors and hips, while engaging the muscles in your legs and butt.
How to do it: Stand with feet shoulder-width apart, toes facing forward. Push your hips back as if sitting in a chair and lower into a half-squat (45-degree bend in your knees). From this position, extend your left leg out to the side, lift it off the ground, and return it to the starting position. Repeat with the opposite leg. Alternate sides until you complete 20 reps.
Variation: Try extending your leg to the back instead of to the side.