Wolfram|Alpha now allows you to explore and compute U.S. retail sales data so you can better understand these trends. "Try simply asking Wolfram|Alpha about "U.S. retail sales" and you'll see the latest monthly figure, along with automatic computations of that number as a per capita value and as a fraction of total U.S. GDP, as well as the annual growth rate for overall retail sales. To filter out the seasonal variation in many sales categories, you can also ask for "seasonally adjusted retail sales" —which more clearly shows the retail sector's dramatic plunge in late 2008," informs Wolfram.
You can explore trends in individual retail categories (click "More" in "Retail sales categories" pod for detailed list), such as clothing stores or electronic shopping and mail order houses. Or mash up this retail sales data with other economic data in WolframWolfram|AlphaAlpha. Try comparing retail sales at building-supply dealers with housing starts.