Oprah has a nice feature on her website right now that links to information on organ donor information in every state in the U.S. Here's the link.
I wouldn't generally recommend Oprah's site. I think it's pretty outdated and functions more like an old-fashioned slideshow than a modern-day webpage, which is pretty sad considering all of the resources she has at her disposal. But I am a big fan of Dr. Mehmet Oz and the way he teaches health. Organ donation is an issue that we all should think about. It doesn't end up being a possibility for everybody, but for those it is possible for, you can extend life for other people when your life is over. And this link provides a nice, easy way to figure out what you need to do to become an organ donor.
As with any end-of-life issue, if you want to be an organ donor, you should let your family know your decision, so that the situation actually comes up, it's not a surprise and they are prepared to carry out your wishes. Organ donation is still controversial for some—people worry doctors won't work as hard to save the lives of organ donors or just don't want their family members' body parts taken. (And by the way, doctors won't try less hard to save an organ donor.) If your family hears from you directly that it's what you want, it's all that much more likely to actually happen when the time comes.