• iTunes: The iTunes Music Store (www.itunes.com) launched by Apple Computer in April was the big Web hit of the year, selling 25 million song downloads at 99 cents apiece in eight months. It triggered a stampede of announcements from rivals planning similar music stores, including Wal-Mart, Dell, Sony, Virgin and Roxio's revamped Napster.

• Friendster: The Web got a new twist on friendship when Friendster (www.friendster.com) debuted in March. The service lets people develop and maintain elaborately structured electronic networks for making new friends and staying in touch with old ones. Friendster was one of many such "virtual networking" sites debuting with names like Tribe.net, LinkedIn and Friendzy.

• Vonage and Skype: These two pioneering startups are pushing the boundaries of Internet telephony and challenging traditional phone companies.

Vonage Holdings Corp. (www.vonage.com) of Edison, N.J., sells an Internet calling service for $35 a month that lets people place unlimited local and long-distance calls anywhere in the United States or Canada, using regular phones at both ends of each call. Subscribers plug a regular phone and special modem into their broadband Internet connections to place calls.

Skype (www.skype.com) debuted in the summer. The free computer-to-computer calling system uses special software to let users call other people anywhere in the world over the Internet, provided that people at both ends of the call will use Skype's calling software and have Internet access.

• Amazon.com: The Seattle-based retailer (www.amazon.com) added a "search inside the book" feature that lets people search the full text of some 33 million pages inside 120,000 book titles from 190 publishers. The online company also expanded its "Amazon Marketplace" last year to make it easy for any retailers to sell on Amazon.com, and opened new shopping departments, including those for gourmet food, home items and sporting goods.

• Google: The 5-year-old search engine (www.google.com) added software for creating Web logs, or "blogs," and introduced all sorts of other features last year, including a math calculator, ad-blocker and e-mail news alerts. Last month, Google started testing a service similar to Amazon's that lets people search inside books.

• Kazaa: This song-swapping service (www.kazaa.com) owned by Sharman Networks came into its own as the new Napster in 2003. Despite the hundreds of lawsuits the record industry filed against individuals for allegedly sharing copyrighted files online, Kazaa ranked as the Internet's No. 1 search term last year, according to the Lycos search engine. In August, Kazaa debuted a "plus" version of its software that let users pay $30 to purge their file-sharing software of advertising.