Janina Diamond toothpaste (now called Janina Extra strength whitening or something)
http://www.amazon.co.uk/Janina-Extra-Strength-Whitening-Toothpaste/dp/B00742C4QK/ref=pd_sim_d_3
I use nothing else, it's the only thing that keeps my teeth stain-free (recommended by my dentist, it's not supposed to damage teeth over time).
Edit: You might find that electric toothbrushes have a negative effect. For some reason they don't clean stains for me, I have to use a manual toothbrush and apply pressure. I don't even smoke