Ning.com is hottest new Web 2.0 tool to be announced this past week. Ning.com (now in version 2) allows anyone to easily create, through a drag and drop process, a Social Network on which members can post discussion items, blogs, photos and videos, and more. It is entirely free, with advertising, and $19/month without ads. Although it is in no way only for travel and tourism, there were close to 200 social networks that are tagged "travel" on the day that I wrote this.
I have created two social networks of my own at Ning.com. One is centered on my Travelography Travel News podcast (at http://travelnews.ning.com), and the other is on Responsible Travel and Sustainable Tourism (at http://responsibletravel.ning.com).
It was very easy to create these, though doing more customizing will probably take some time. In particular, I would like to add a Google Map mashup, which is found a quite a few of the social networks (such as the Travel Tips one, below). The networks with these maps appear to be from version 1 of Ning.com, and is not a standard tool built into version 2.0. In fact, if anyone has some tips on how to create a map mashup and add it to Ning.com, I would appreciate the help.
For a video introduction and tutorial to Ning.com, go to the Scoble Show blog. Also see Ning reviews on Tech Crunch and GigaOM.
NEW (7 Sept 07): There are other web services similar to Ning that may meet your needs better. TechCrunch.com reviews nine of them here.