Monergism: Calvinism. This is THE PLACE to go. Tons and tons of articles from a huge array of theologians and pastors. Articles, sermons (audio and print), book reviews neatly arranged by author and/topic. Piper and Azurdia’s sermon series are stellar!
Monergism: Doctrines of Grace. This part of Monergism's site also has a bunch of goodies.
Desiring God: The Doctrines of Grace (Calvinism & TULIP Theology). Articles, sermons, and products.
Desiring God:What We Believe About the Five Points of Calvinism."Most recommended for a comprehensive explanation of the doctrines of grace. About 25 pages.
The Calvinist Corner. Not really sure about this one, but what I’ve seen I like. Like anyone who goes by the title “Calvinist”, you or I may not agree on every detail or argument. One example: I still don’t find his argument on infant baptism convincing. What can I say, I’m a good Baptist! In short, I believe the covenant oath sign of the New Covenant is the circumcised heart by the Spirit, not baptism. Nevertheless, this guy is very helpful.
Tim Challies: What It Means to be Reformed. He says quite a bit more but here’s his conclusion: “So what does this all mean? To be Reformed is to adhere to the purist teachings of the Bible - to affirm the doctrine taught by Jesus, Paul and the apostles.”
Spurgeon.org: A Letter from George Whitefield to the Rev. Mr. John Wesley.A blast from the past. Here is a great dialogue between two brothers in Christ who did not agree. Whitefield is an excellent example of how silly it to "logically deduce" that the doctrines of grace squelches evangelism and deadens urgency.