* Faceparty: The U.K.-based "Biggest Party on Earth" is often referred to as the British MySpace. The site sells subscriptions for premium content (Cool Tools) as well as advertising space.
* Friendster: The grandparent of the social-networking space born in 2002 is still hanging around with some 27 million members. It even launched an updated version last fall that it dubbed Friendster 2.0.
* Xanga and LiveJournal: Remember when parents were afraid of these two sites? That was before MySpace took off, but these two similar sites cater more to journal writers and blogging than purely social interaction.
* LinkedIn: Specifically targeted at business professionals and their work networks, the site makes money by selling premium services with fees ranging from $60 to $200 per year for different levels of contacts. It also sells job postings ($95 for 30 days) and, of course, ads.
* Yahoo 360: Use your Yahoo ID as entry to this social-networking site that combines blogging, messaging, instant messaging, photo and music sharing in an attempt to create a one-stop social site. It's only a year old and still in beta format, but worth watching.
* Orkut: Computer programmer Orkut Buyukkokten developed the invitation-only site while working at Google during his company-encouraged 20% personal-project time. The Google affiliation alone makes it one to watch, although since it was launched in 2004, it has failed to capture widespread U.S. interest. However, it is "the" social network in Brazil, with some 11 million of Orkut's 15 million members living in the South American country, according to published reports.
* Wallop: Microsoft's entry into the arena can't be ignored. Just announced recently, Wallop was spun out of Microsoft Research into its own company. The Wallop product won't launch until later this year. No word yet on how Wallop plans to generate revenue, although Microsoft executives have said it won't depend on advertising.
* And if you're in a surfing mood, here are a handful of others that rise nearer to the top of the heap in social-networking-savvy conversations: Bebo, Ryze, Tribe.net, Gather, Tagged, TagWorld, VarsityWorld, Imeem, and Rabble.
So how much does it cost to advertise on them? Rates appear to be fairly fluid. An informal consensus of online media buyers agreed that a $10 CPM asking price seemed about average, although they also agreed that could vary greatly depending on quantity bought, ad size, placement, and frequency. One buyer said, "MySpace was just in here pitching us, and they didn't really tell us [CPM rates] either."
(A recent New York Times article said there are deep discounts on MySpace and quoted parent News Corp.'s Fox Interactive Media chief Ross Levinsohn as saying average ad rates on MySpace currently average about 10 cents per thousand impressions.)