If you're among the folks who plan to shop online this holiday season—some 44% of adults, according to a survey by the Consumer Reports National Research Center—the next few days are important to getting your purchases shipped at minimal cost and with maximum assurance they'll arrive by Christmas.

While the deadline for free shipping has already passed for some retailers, many others have deadlines of tomorrow or Thursday to place free-shipping orders that will arrive by December 24. Most notably, tomorrow's the deadline to place such an order that qualifies for free shipping with Amazon.com, the online giant that's among the higher-rated websites in our Ratings of electronics retailers (available to subscribers). The company will fill orders with standard shipping on the 18th and still guarantee delivery by the 24th, but you'll have to pay the shipping yourself.

Also, as Tightwad Tod, our frugal-shopping guru highlighted recently, Thursday is being billed as Free Shipping Day, with a host of retailers supposed poised to offer no-cost shipping on orders placed that day, with delivery guaranteed by Christmas Eve. Many participating merchants are already listed on Freeshipping.org, the site that's coordinating the effort; others may announce their participation late, in order not to dampen sales over the next day or so. The site also provides a handy one-stop list of shipping deadlines for many websites.