Invision Power Board is great. The Blog or Gallery or other modules are written by 3rd parties mostly and not the same development team that writes the Forum product. It might be a lot more resource intensive than necessary to run a good size community blog.
Look into Drupal.
http://www.drupal.org/
Example sites:
http://www.freejournal.net/drupal/
http://www.irishblogs.org/