iMIS Communities is ok
We switched to iMIS a couple of years ago from a homegrown AMS. Included in iMIS is iMIS Communities. It includes unlimited communities with announcements, discussions, blogs, wikis, and resources. Our members have not taken to it because it isn't super-easy to use. It seems that ASI has not devoted much attention to this part of its software offering, so no new developments have been made since we launched the software. One of the biggest issues that staff have with this software is that it doesn't give the option for a daily digest, and every time someone posts something, everyone gets an email, even when a post has been edited after it is published. That's a lot of potential email during the course of a day.
If you have a staff-person dedicated to managing your online community and resources are tight, iMIS Communities would probably work fine, at least in the short-term.