Eternal Word Television Network Website
http://www.ewtn.com/

The Pope's Official Vatican Website
http://www.vatican.va/

Defense of the Catholic Faith

Catholic Answers
http://www.catholic.com/
Bible Christian Society
http://www.biblechristiansociety.com/
Defenders of the Catholic Faith
http://www.catholic-convert.com/
St. Charles Borromeo Website
http://www.scborromeo.org/index2.htm

Scriptural Support for Catholic Doctrine
http://www.scripturecatholic.com/

Dr. Scott Hahn's Biblical Theology Website
http://www.salvationhistory.com/

The free Catholic Online Encyclopedia
http://www.newadvent.org/

Papal Encyclicals
http://www.papalencyclicals.net/

And this one gives reviews of a lot of other websites to know whether a website is a good one or a bad one.
http://www.catholicculture.org/