When I take a shower, I hold one capful of 3% hydrogen peroxide in my until it's time to rinse my hair (at which time it's helpful to have my mouth for breathing, anyway...). My dentist has commented more than once on my bright teeth and healthy mouth!
Bentonite clay works too and is reportedly remineralizing. Peroxide is bad for the enamel.
The lady on Gypsy Sisters used bleach! She's nuts. I heard baking soda works well too.