Back when I was planning my wedding, I remembered reading that you could invite the President to your wedding and he would send back a letter of congratulations in return. So I did that and President Obama sent me a really nice card in the mail.
sorry for the blurry photo!
If anyone is interested in getting a keepsake like this, you can mail a wedding invitation or birth announcement to:
White House Greetings Office
Washington, DC 20500