In patch 2.0 you can join 1 clan, and an unlimited amount of communities.
Feel free to join the MMO Champion community in game (Up in NA & EU)
How to join a community:Communities are designed to be a place where players can come together for any number of reasons, including playing the same class, frequenting the same fan sites, or living in the same geographical area. They're all about fostering relationships between like-minded people, with a keen focus on socialization.
Unlike Clans, Communities are intended to be much larger and more casual. They can be public or private, for example, and support a nearly unlimited number of members. In addition, while you can only join a single Clan, you can be a member of multiple different Communities at the same time.
1. Shift + O to bring up the community menu (bottom right of game screen).
2. Hit "Find Community"
3. Search for "MMO Champion"
4. Hit Join
No approval necessary.
Note: You will not be in the chat unless you turn it on. When you open your communities you will see a red icon or green icon next to the name. Click it to join (green = in chat, red = not). This needs to be turned on every time you launch Diablo 3 as it defaults to off currently.
Our sister site Diablo Fans also has a much bigger community so you may want to join that too