Denominational sites:
Reformed Church of the United States

Other Reformed sites:
Orthodox Presbyterian Church
Presbyterian Church in America
Canadian & American Reformed Churches
Reformed Churches in the Netherlands
Reformed Presbyterian Church of North America

Reformed References:
Center for Reformed Theology and Apologetics
Ligionier Ministries (RC Sproul)
Alliance of Confessing Evangelicals
Reformation Society of the Twin Cities
White Horse Inn
The Hall of Church History
Calvin On-line