Roman Breviary in Latin and English
This site has the complete Roman Breviary in Vulgate Latin and traditional thee-thou English, as well as good commentary and the Martyrology, the Ordo, and other prayers and devotions. It follows the rubrics that preceded Pope Pius XII's interim changes.

Haydock Commentary
The Haydock site contains the Haydock's commentary online. Most of it is done. All of the New Testament and most of the Old have been completed. They are always adding more, so they'll probably be done within a year.

Douay Rheims with Challoner's revisions
The Intratext website contains the Douay Rheims translation of the Latin Vulgate, with A rchbishop Challoner's revisions. You can search alphabetically, do a search on which verses in the Bible contain the word you are looking for, do a search on how many times the word is used in the Bible, etc.

Douay Rheims online
The Douay Rheims translation of the Latin Vulgate, with a Latin version as well.

Papal Encyclicals
Your guide to online Papal and other official documents of the Catholic Church.Has most, if not all the Papal encyclicals, and allows you to search by Pope.

LITURGIA LATINA
This site is the fruit of the scholarly research and devotion of David Foster, a British Catholic. It has many interesting and valuable texts, such as the Roman Martyrology. The site also has also republished books that are particularly valuble to devotees of St. Philip Neri, and other works with which all Catholic should be acquainted. It also features some excerpts from the Carmelite and Dominican Rites.

Thesaurus Precum Latinarum
This site has many Latin prayers along with English translations. Michael Martin has compiled some very interesting and obscure devotions and prayers form old libelli precum. Traditional Catholics should be able to pray at least the most important prayers in the sacred tongue of the Holy Roman Church.

Breviary Texts
Online texts of all breviaries existing today. Has the Ambrosiam Psalm scheme, the Little Office of Our Lady and many more.