I have a friend who has always had beautiful white teeth.
When I asked her some years ago how they stayed so white, she said that when she was a child her mum used to make her brush her teeth with baking soda (tasted horrid) but she still used the Arm & Hammer toothpaste with baking soda (tastes nice). I swithed and it did make my teeth look much whiter.
... tell you what does make a difference - I got a Phillips Sonicare brush for Christmas and they DO clean your teeth far better than conventional brushing.
try Dentyl the visibly active mouthwash you wont believe what you leave in your mouth after brushing and teeth feel clean all day its excellent and floss always floss