When it's time to consider bathroom lighting, keep in mind that most accidents in the home occur in the bathroom. For this reason, if for no other, it is much better to over light than under light your home's bathroom.
For very small bathrooms and powder rooms, wall sconces on either side of the vanity mirror or a multi-bulb vanity light above the mirror may suffice. However in a medium to full size bathroom you'll want to supplement the vanity lighting with a flush or semi-flush mount ceiling light fixture. Remember even with a bright ceiling light, you still need the wall mounted vanity lighting to provide proper illumination for grooming tasks such as shaving and putting on makeup.
Other smart options for bathroom lighting include fixtures mounted above shower stalls and bathtubs. If your bathroom is also the place you go to get away and relax, you should seriously consider wiring some of the lights to separate dimmer switches so that you can dim or brighten the lighting to suit your comfort level and the task at hand.