Desiring God is a comprehensive Bible-saturated resource site providing sermons, articles and free ebooks by John Piper.
Ligonier Ministries is an international Christian education organization founded by theologian Dr. R.C. Sproul to equip Christians to articulate what they believe and why they believe it.
The Gospel Coalition is an association of evangelical churches and ministries centered on the gospel of Jesus Christ. It has a very active online presence with a whole host of blogs, articles and video interviews.
Together for the Gospel is a ministry that aims principally at encouraging evangelical pastors, no matter their denomination, to stand for the gospel.