tooth whitening is one of those things that the less you spend, the less results you get. if you're paying under 50 bucks for a product you probably won't be happy with the outcome. I'll list some good options:
-In office laser technique: the goods: good results and very time efficient, but you gotta go to the dentist and pay a fair amount for this.
-Bleaching trays: your dentist makes you a set of custom plastic trays that you put the tooth whitener in (usually carbamide peroxide, this is not bleach) and wear it (usually overnight). I personally use this, it's somewhat time consuming since you need to do it for a couple weeks usually to get max results, but they turn out real good, better than strips.
-Crest White Strips: very popular, you sort of tape this strip onto your teeth for a while and you get pretty decent results. this is probably the cheapest way of tooth whitening, BUT... you really need to go through 2-3 boxes to get the best results (and then keep doing another box every few months). You can buy these at any CVS, however your dentist can get you the professional strength ones which are MUCH better at getting the job done.
But seriously, anything you buy off an infomercial, the bargain bin, or some swap meet is probably a waste of your money. If you want whiter teeth Crest White Strips are the only thing you can buy over the counter that will do a good job imo. Also if you are one of those people who never ever go to the dentist and get some whitening products, I don't recommend it. Whitening can make some people's teeth very sensitive and painful and if you have dental issues (ie decay, cavities) it will only make the agony worse.