Here are the few online communities that helps me get some traffic to this blog. Although i don't use Myspace, it is known as one of the biggest social network to built communities. But here are couple that use regularly, also helps:
MyLot: As well as building communities, it also pays you to post questions and to answer others' questions. You won't get rich, but you can make enough to pay your Internet connection or any other small house hold bills.
MyBlogLog: Share views with other blog owners. You can join to many blog communities and built network of friends. It also has some cool widgets such as Recent Reader (shows, who is reading your blog), Top Links (shows top referrer to your site), and Stats Tracking (shows stats and links clicked on your site).