Catholic Answers – EVERYTHING you could ever want to know about the Catholic Church. They have a magazine, articles, a radio program (all the show archives are online, for free), an enormous discussion forum, videos, tracts, documents, a shop, and they have conferences and cruises and a publishing house.
About.com – Catholicism – A whole lot of resources, especially the basic stuff. They list a lot of Catholic “cultural” things, like the prayers used, and the holy days, as well as important people and historical occurrences.
Catholic Online – I particularly like their encyclopedia, and their information on saints and prayers; you can get information on almost anything.
Unites States Conference of Catholic Bishops – Good resource for official Catholic policies in the United States (yes, they can differ from country to country).
The Holy See – The official Vatican website; this is the place to find the definitive word on all things Catholic. Using the search box, you can find official documents on everything the Catholic Church has ever said.
Vatican Player – Live video from the Vatican; you can watch the Pope conduct Mass and give speeches (or whatever it’s called when the Pope comes out and talks to everybody).
The Vatican YouTube channel – Excellent videos of pretty much everything the Pope does.
National Catholic Register – A Catholic news source. Also home to blogs by several good writers, including Jimmy Akin and Jennifer Fulwiler.
Why I’m Catholic – An excellent compilation of personal conversion stories, organized by the belief the convert came to the Catholic Church from: from atheism, from Baptist, from Buddhism, etc.