Tom's of Maine whitening gel toothpastes are absolutely fantastic! I brush my teeth at least three times a day, and have tried nearly every brand out there - but most of them leave my mouth feeling chemical. Tom's of Maine is much better, as it's all-natural.
The flavors are all great (personally, I like cinnamint), they are flouride-free, not tested on animals, and free from other chemical ingredients. The only downside is that the packaging is aluminum, and can be difficult to squeeze as the toothpaste runs out. Also, the flavor isn't long-lasting, but that's a fair trade in for the lack of chemicals, if you ask me.
As for the whitening? I've noticed a slight change since I've started using the toothpaste, but given that it's all natural, it probably won't be as effective in that area as a chemical product would be - but again, for a natural product, it does a good job.