Give to a group that has an unequivocal message on this The Brady Center. I just gave $50 to them and I urge you to give also, if not to Brady, to another gun control group. Have patience -- the site loads a bit slowly, probably because they're getting flooded with donations.
The definition of insanity, in this case is not doing something and expecting that something will not happen again. And the politics of guns in this country is nothing less than insane.
I still feel depressed and infuriated, but just a little less helpless, having given.