Two new places I learned about at the Berkeley New Media Conference were Neopets and Whyville.
Neopets is a place where kids create virtual pets, enter them into contests, build community, etc. etc. Neopets is apparently huge, drawing large numbers of visitors for very long stays. Large as in rivaling the major sites (CNN, ABC, Yahoo). Long as in approaching a couple of hours a day.
Whyville is oriented towards math and science education. While not quite garnering the same numbers, the number of females on Whyville is striking. In the early phases of the site, they had a close to 60/40 split in favor of girls. With some tweaking they've made it closer to 50/50, but there are still more girls and they are very active participants.
There are two striking commonalities of these sites. First, neither does any marketing. In fact, the organization behind Whyville is ridiculously small. (I'd tell you, but then I'd have to shoot you).
Finally, and much more relevant to NMH, both communities wind up reconstructing the concept of a newspaper institution. Whyville has the Whyville Times, and Neopets has the Newtopian News, if I remember correctly. (Correction: Neotopian News)
Memo to self: smells like a paper to me