At the same time, online companies such as Amazon.com, Yahoo and PayPal did their part to help out in relief efforts, allowing companies to make online payments directly to the Red Cross.
Perhaps most affected by the disasters were the online travel sites. With air traffic halted nationwide and thousands of flights canceled, such sites saw transactions slowed and customer service centers swamped with calls.
Because the Federal Aviation Administration has yet to lift the ban on air traffic, Priceline.com, which gets much of its business from last-minute travelers, has stopped taking new reservations through this Sunday, company spokesman Brian Ek said. Ek declined to say how that had affected the company's business, but Priceline gets more than 90 percent of its revenue from travel-related sales.
For customers already holding tickets, Priceline is directing them to first contact the airlines directly about refunds and cancellations.
"If for any reason you can't make it to your destination, call and we'll work with you," Ek said. "We're going to abide by what the airlines decide to do."
Competing airline site Expedia also is getting a lot of calls and has stopped taking reservations for flights departing before Sept. 18.
Spokeswoman Suzi LeVine said Expedia will try to help customers cancel tickets or get refunds even for tickets that previously could not be canceled.
Orbitz continues to take reservations, but there are few takers.
"Less people are buying online in general and I think that's also true for brick-and-mortar goods and services as well," said Stacey Spencer, an Orbitz spokeswoman.
Grounding the nation's planes has also stalled deliveries for online businesses and auction houses. Air cargo comprises about 40 percent of the value of world trade, and e-commerce companies depend on it for shipments both from their suppliers and to their customers.
Online auction giant eBay warned members of Post Office closures and possible delays in receiving packages. E-tail leader Amazon.com said that while it doesn't expect the groundings to affect the shipments it receives from suppliers, the company will delay overnight deliveries to customers.
Meanwhile, the United Parcel Service warned customers on its Web site that the bombings would cause some delays throughout the country for an indefinite time.
As package delivery slowed, so did some online transactions. At the same time, many Web sites turned over large amounts of space to urge people to donate to the Red Cross.
By midday Wednesday, Amazon customers had donated nearly nearly $800,000 to the Red Cross through Amazon's online payment system. Several other online companies, such as PayPal and Yahoo, set up similar payment systems. The Red Cross also directed some visitors to Helping.org, a nonprofit group set up by Internet and media giant AOL Time Warner, which lets people make online donations to a variety of charities.
Some online auction sellers apparently attempted to cash in on the disaster, listing World Trade Center and Osama bin Laden-related items on eBay and Yahoo's auction site. A search for "World Trade Center" on eBay, for instance, turned up 47 postcards, T-shirts, newspapers and other items. A similar search on Yahoo revealed five items.
eBay and Yahoo both announced a ban on such items and canceled the auctions. eBay said it would ban the sale of any items referring to World Trade and Pentagon until Oct. 1.
On Amazon, books related to the World Trade Center Twin Towers or terrorism jumped to the top of the company's best-seller list. The No. 1 seller on Amazon was "Twin Towers: The Life of New York City's World Trade Center," according to Patty Smith, an Amazon spokeswoman.
Also among the top 10 sellers was "The New Jackals: Ramzi Yousef, Osama bin Laden and the Future of Terrorism," a biography of the men who allegedly masterminded the 1993 bombing of World Trade Center.
"Anytime you have a major news event, sales of books with anything to do with the subject skyrocket," Smith said.
Staff writer Margaret Kane and Reuters contributed to this report.