I am a certified fitness instructor and personal trainer, and Want to agree with Kristen and Lizzie's responses that cardio is a good choice for you. "spot reduction" (i.e., reducing just your middle though) is a myth; read more here -- Link. Walking, biking, stair stepping, spinning, ellipitcal - all of these are cardio choices that use the large muscles in your legs. By default, all of these cardio choices will tone your legs. You should see nice improvement if you stick to a regular routine.

Cardio is always the first thing to do, definitely. You can follow that up with targeted toning. Try a pilates or dance class, or ask a trainer at they gym to show you a few exercises that concentrate on your overall lower body strength.

From everything I've read, cardio is the best way to shrink your body overall. Any muscle building exercises will only bulk up the spot you're trying to minimize. Have you tried doing more walking or bicycling?