Go to your dentist. When she asks if you have any concerns, tell her that you don't really, but you wouldn't mind having whiter teeth.
At some point she will say that their dental office is trying out different bleaches and you seem to be a good test subject.
(I forgot to mention that you might get indirectly insulted about your yellow teeth along the way.)
Say, "Okay," and forget about it.
At the next cleaning she'll tell you they're ready with the bleaches and you can come in the next day if that works for you.
(I also forgot to mention that it involves bleaching half your teeth with one brand and the other half with another, so there's a potential of coming out of it looking like you're wearing a mouth guard of some team whose colors are off-white and off-off-white.)
Bring your iPod, doze off in a chair with your mouth held open for two hours, and tadaaah!
(I also forgot to mention that she will say some things about potential temporary chemical burns on your gums in a very offhand way, making the initial sitting still period a little difficult.)
And you're done! Total cost: two subway rides and a handshake.
I went from an A3 to a B1. (Does that sound right? It's what I remember, anyway. Does that mean anything to anyone? Those were the colors of teeth that she thought matched mine.)
But if I'd been told beforehand that I'd have to sip my coffee or tea through a straw because they are sensitive to staining for a while, I'm not so sure I'd have agreed.
If I seem extra grumpy, it might be the *&%$!! caffeine withdrawal.