Just a quick preface to this, so that you don’t have to find out the hard way (like I did): If you have sensitive teeth, you probably don’t want to use any sort of home whitening kit. Ouch.
But! If you are in the market for such a thing, trot on over to Soap.com, where right now this Crest 2-Hour Express Whitening Kit and Rinse bundle is $55, but coupon code FBCREST3D will save you 50%. That takes it down to just $27.50, which means it also qualifies for free 2-day shipping.
For reference: The box of strips alone is $35 direct from Amazon.