What exercises can I do to tone my butt and upper thighs?

I'm naturally thin but I have noticed lately that my butt and upper thighs are kind of scary. I actually have cellulite there, which is really frustrating. I'm not someone who goes to the gym to work out, so simple exercises I can do around the house would be nice. I do try to walk about 3 miles each day, and I eat a healthy diet.