Operated by Mark Dever and Matt Schmucker, 9 Marks has proven to be one of the most valuable assets for church leaders today. Their website is very extensive, featuring articles and a helpful walk-thru of the 9 Marks of a healthy church, including brief audio answers about how the 9 Marks should be implemented and common questions that arise. They have successfully pooled the wisdom of many godly, experienced pastors.
The highlight of the site is the extensive audio collection, most of which are interviews and discussions with pastors and theologians about current topics, mostly related to the health of the church. If you are a pastor, elder or interested in ministry, this is one site you need to frequent.