Tom's of Maine is a popular fluoride free toothpaste. Burt's Bees also has one. And some people even use Dr. Bronner's liquid soap to brush their teeth. The peppermint and tea tree oil varieties are the most popular for that.

Edited to add; writing that reply reminded me that I wanted to start using Dr. Bronner's soap again, so I went to their website to order. And I see that they're making their own toothpaste now. They have peppermint, spearmint, cinnamon and anise flavors. I think I'll buy a tube and see how it is. Because I was never a huge fan of using soap to brush my teeth. It was nice only having to pack one bottle of soap when backpacking, though. Shampoo, body wash, toothpaste, laundry detergent, and all purpose cleaner all in one bottle.