My most highly recommended whitening product for the past 8 years has been Crest Whitestrips. They have been around for a long time, are affordable and highly effective. If you are still unsure about which whitening product to try, I would push you to buy Crest whitestrips online.
Where Can I Find Them?
The two easiest places are Amazon.com (for my American readers) and Amazon.ca (for my fellow Canadians).
I have to admit that I am an Amazon junkie. If I can find it on Amazon, I buy it on Amazon. For me, it is all about the convenience of being able to find everything I need in one place. That being said, there are a number of online retailers that sell Crest Whitestrips. I will place links below for all of the reputable U.S. and Canadian sites that I could easily find that carry these products.
If you are looking for a specific line of Crest whitestrips you may have to check multiple sites. It does not appear that everyone carries all available products.
Shopping in the United States
Shopping in Canada
Teeth Whitening at amazon.ca