I have a gray cast to my teeth, so I've tried lots of tooth whitening products. The toothpaste I like best in this category is Colgate Simply White. I like that it's by a name brand that I trust. I also like that it's gentle to use. I've used other whitening products that have actually caused the inside of my cheeks to start peeling. Simply White comes in two flavors and costs about $4.49 a tube. I never pay that much, though, as there are usually coupons or sales where I pick it up for less money.
The one complaint I have about this product is that the application is messy. The tube is divided into to main sections, one with each main ingredient. The idea is that these ingredients aren't supposed to touch until you squeeze the tube to put it on the tooth brush. What often happens is one side comes out but you have to mess with it to get the other side to come out of the tube. Other than this, I do feel the product provides effective whitening when used on a regular basis.