On Sunday, May 13, most Americans will celebrate the extraordinary woman in their lives — Mom — with a perfect outing and a gift or two. While mothers certainly look forward to the annual pampering, retailers anticipate the holiday even more. That's because the money spent on meals, cards, flowers, jewelry, and other presents adds up to billions of dollars, making Mother's Day the third largest retail holiday in the U.S., behind only the winter holidays and back-to-school season. Even better? The spending keeps increasing year after year.