I would second A&H!
Have used all the usual suspects, and even they're most of them are okay, I just felt I needed to find alternatives and give the smaller guys a chance.
Encouraged by positive reviews on Amazon I went for A&H Extra White (I think it was a 6 pack for about £8). Great taste, slightly gritty, but certainly made a difference to the whiteness of my teeth!
Of course I don't know if it actually properly protects/cleans my teeth in the same way as say Colgate, but I've been using it for about 24 months and have never had any issues at dental check-ups.
I think there's all different types of A&H paste, including baking soda.
Definitely give them a try