Everyone can read the official forums (without membership). Everyone can join and post. The forum uses Google accounts. No registration is needed if you want to post (just a Google account; if you have a GMail account for example then you already have one). If you don't, create one.
General discussion forum:
https://groups.google.com/d/forum/sc2gears
Developer discussion forum:
https://groups.google.com/d/forum/sc2gearsdev
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External Sc2gears forums and discussions
Main thread @ Teamliquid.net: Sc2gears