And sign that damn donor card!
In Washington and Oregon -- don't know about other states -- you can indicate your desire to be an organ donor on your driver's license.
Even if you have an organ donor card or the mark on your license, it's important that you discuss your wishes with your family, because they have veto power. If you're dead, you've indicated you want to be a donor, and your next-of-kin objects, they won't cut you up and pass you around.
As for me... I've got the mark on my license and I've had the talk with my family. I figure once I'm gone, I'm done with my body and if someone else can make use of the parts, they are welcome to them. I have friends who are alive today because of organ donors.
And in case you were wondering, you can still have an open casket at your funeral even if you're missing a few internal parts.