Just so everyone knows, it's painless, easy, takes only about an hour of your time, and you could save somebody's life. Your body just makes more of it afterwards. It's a no-brainer as far as I'm concerned. You could be helping anybody from a car crash victim to a tiny little newborn baby in need of something that you already have and won't miss.
I encourage everybody to take a second and consider donating blood at some point in their life. Wouldn't you want to be able to receive a transfusion if you needed it?