It's tricky to find many well-designed community sites on Drupal (or at all).
Too many focus on content. They place the content at the top of the page and bury the community either beneath the fold or behind a community tab. This might look great, but it's not effective for building communities.
Plugincars is a notable exception.
This site balances the content, with the community, with the current activity. If they removed the advert in the top right, it would be perfect.
There are five things I want to highlight here:
1) The content appears on the landing page on a regular basis. Members always have a reason to come back and visit the community to see what's new.
2) The community appear highly active. They choose to show the number of discussions, photos, fans etc…this gives the impression of momentum.
3) The latest discussions also appear on the right of the page. This shows the latest activity that members can immediately click to participate in.
4) The community balances the social needs with the need for information. In addition to the landing page, members can see guides that they can download.
5) The community also seperately lists the one key thing that members want to know, where can they charge their car? What is the one key, major, thing the members in your community want to know?
Also note that within the guides themselves they have guides for people that are new to the topic and for those looking to purchase cars. Most communities neglect the people that are new to the topic, yet it's these people that will be the biggest source of growth for most mature communities.
Plugincars also does a great job of highlighting the key contributors to the community. This is on the landing page of the community.
Finally in the cars section of the community, they give an instant overview of the topic. They provide a list of rechargable cars, upcoming cars, and the basic details of each car. This provides members with a glance of most of what they want to know about the topic.
If you're looking to build a great community on Drupal, Plugincars is a good place to start.