before you add extra lighting, i would say paint it. something white.
it is amazing how much the color of your walls will effect the lighting in a room. not to mention, a can of paint is probably cheaper then new lights. ive done this a few times with different sheds/garages/workshops and every time, a simple coat of paint made a huge difference.
still want more light after that? i would personally go florescent. a few well placed 48" lights will be plenty.