I've used the Crest White strips, you can get them from Walmart, K-mart or Target. I can tell you that this product worked for me 100%, I use them and my teath are SOOOOOOO much whiter, Good luck!!!!
You can purchase kits in stores like Wal-Mart, K-Mart, Target, Etc., but they will only whiten about 2 to 3 shades, TOPS. If you are looking to dramatically whiten your teeth, you would need to obtain a kit from your dentist. Also keep in mind that if you have any white fillings or crowns, they will not bleach with ANY system you can buy. Hope this helps!