For historical Reformed documents The Center for Reformed Theology and Apologetics is an excellent resource, especially if you click on the Historic Church Documents header.
For a general introduction to Calvinism I would recommend:
"The Bondage of the Will" by Martin Luther, not surprisingly Luther was a Lutheran and not a Calvinist but this is a great book that shows the almost universal agreement of the reformers over the Doctrines of Grace.
"What Is Reformed Theology?: Understanding the Basics" by R C Sproul is a really top notch introduction to Calvinistic theology.
"The God Who Justifies: A Comprehensive Study of the Doctrine of Justification" by James White is a fascinating study of the Gospel, too many Christians have no idea why they are saved and therefore really do not understand why they should be thankful, this book explains why.
"The Sovereignty of God" by Arthur W Pink is a classic study of God's sovereignty. Pink was a flawed man but his whole life was as a humble servant of God and he never strayed from this central truth and we should be encouraged that in our weakness God finds strength. make sure you get the Baker edition, the Banner of Truth edition was "edited" to remove elements that the editor disapproved of. Do yourself a favour and make up your own mind from the full text. Incidentally the reason for the two versions is that Pink did not copyright his writings, now that man trusted God's sovereignty.
www.toplady.org.uk is my site dedicated to that great calvinist Augustus Montague Toplady