If you are a frequent Amazon.com shopper, you might want to consider Amazon's first membership program, Amazon Prime. For $79 a year, you can enjoy free two-day shipping for most of your Amazon orders for the entire year. Plus, you are entitled to $3.99 per unit one-day shipping during your membership period too.
What's more, you may "invite up to four eligible family members living in your household (at the same address) to register for Prime membership at no extra cost."
Now to the fine prints: first, not all products are eligible. According to Amazon.com's program FAQ:
"Eligible products will be designated on the product page, in the order pipeline, or at check-out. The program is limited to products sold by Amazon.com. Some Amazon.com products are excluded, including, for example, oversize or heavy items, items regulated as hazardous materials, and other items with special shipping characteristics. Products sold by third parties, or through third-party areas such as Marketplace, Auctions and/or zShops, are NOT eligible."
Second, free shipping is only applicable to eligible "that are shipped to continental United States addresses, excluding Alaska, Hawaii, P.O. boxes, APO/FPO and U.S. territories, possessions and protectorates."
I don't shop much at Amazon because as a Washingtonian, I had to pay sales tax on all Amazon orders. However, it might be a really nice deal if you made a lot of impulsive purchase last year at Amazon. (If you can always plan your purchase rationally, you can save on shipping without paying $79 upfront by choosing the free shipping option at Amazon site -- also available for most products. Your order may come in about 7-10 days though.)