I got a free sample of Eco-Dent tooth powder yesterday and oh my gosh, it's awesome. I think this is my new favorite green product. You use a tiny bit of the powder on a wet toothbrush and it foams up when you brush. My teeth felt like I just had them professionally cleaned when I was done because they were soooo smooth. I tried the mint and the taste was pretty light and it didn't leave a strong aftertaste. The mint flavor gets a 2 on the EWG website (other flavors get a 4).
As an added bonus, it's cheaper per use than regular toothpaste. They say a 2 oz. bottle gives you 200 brushes and it was comparably priced to Tom's of Maine, Jason, etc.