Honestly the only thing that will give you a dramatic change is bleaching trays from your dentist. You have molds done on your teeth at your dentist's office so they can make trays that fit your mouth, and then you get tubes of bleach that you put into the trays and wear them anywhere from an hour to overnight. Normally this kit is really expensive, a few hundred bucks, but my dentist just ran a special on it - trays and 6 tubes of bleach for $180. Also my dental insurance ended up covering half of it so that was awesome. I am a teeth grinder at night and I need a mouth guard anyway...I figured if I have to wear a mouth guard I might as well have super white teeth! Not to brag too much but my teeth are really white, and it doesn't take more than a few weeks to get them that way. :)
Also I believe there is a laser whitening treatment you can have done at your dentist, but I'm a coffee and red wine drinker so I wanted an option that would allow me to continue to whiten when needed.