My favorite by a country mile is Qlubb (http://www.qlubb.com). It’s geared specifically for “real-life groups” — basically people who interact with each other physically as opposed to those virtual communities like Ning (although Ning can be used for local groups too). The nice thing about Qlubb is that it is dead simple to use and it has other planning features needed for physical, “off-line” groups. Qlubb is more for a private group though as opposed to a location-based community that anybody can join.