Biblehub.com is an excellent resource for those who want to know what the Bible actually says. You can compare many different translations of the Greek or Hebrew original text, and can see the original words used. Strong’s lexicon is fully integrated. There is an extensive library of literature from the patristic fathers to the present, as well as several commentaries. Everything is cross-referenced and opens with a single click.
The Catholic Encyclopedia is an invaluable asset to anyone who wants to look at the official Church position on innumerable issues back to the early church. There are many excellent articles on the every aspect of the faith as well as comprehensive information on church history.
A great resource for those interested in the Apostle’s Creed is http://elbourne.org/creed/. There is a word-by-word interlinear translation of the Greek with Strong’s lexicon hotlinks.