IMUG Email List
This is THE place to be. This is one the most active Media Users communities on the internet. This list is hosted by the IMUG and is extremely easy to subscribe to (and unsubscribe from). There are also searchable archives of all list traffic.

CreativeCOW.net
When Ron Lindeboom left Digital Media Net, leaving the WWUG behind, he and his wife Kathlyn started again with Creative Communities Of the World (COW) with strong community based chat forums with a fantastic array of How2s and Tutorials. Most of the industry experts who previously hosted WWUG forums moved their forum hosting and expertise to CreativeCOW.net. The Media 100 forum is very active and a great place to get assistance and help for Media 100 and all the associated applications. Some of the forums are co-hosted in part by active IMUGGERs Philip Hodgetts, Jeff Handy, and Bouke Vahl. There's a forum for almost every aspect of production that you can think of.

Postforum
Postforum Digital Video Resources is run by Perry of Kinopravda productions, features discussion forums about many digital video topics (M100 and AE included), articles, and a user gallery. This site offers a great number of discussion boards with friendly, helpful people.

DMNForums
Another expansive online group of forums covering a wide range of production areas. They are particularly deep in articles written by industry professionals on topics ranging from software how-tos, reviews, and editorials.

Learn Dynamic Media
This site is created by Aussie IMUGGER Philip Hodgetts, the author of the fine "Media 100 i Companion" reference based on the same approach and technology of the DV Companion for Final Cut Pro. The learndynamicmedia.com site contains an excellent Tips and Tricks section and downloadable output modules and render settings for Adobe After Effects/Media 100. Since locating in the US, Philip has another site www.IntelligentAssistance.com dedicated to the Intelligent Assistants/Companions.