This category of links on the sidebar take you to non-blog websites which I think are excellent (spoiler!) resources. Many of them provide quick access to very important writings.
The first is Bible Gateway. This site's value lay primarily in that it contains numerous translations of the Bible, including 20 in English, combined with a search engine to find words, phrases, subjects, or particular verses.
The Catholic Encyclopedia is next. This is an incredibly extensive collection of articles on church history, theology, and all things Catholic. It's excellent, although most of it was written pre-Vatican 2, which means it doesn't have an inclusive view towards Protestantism. But it's still an excellent resource, and highly recommended.
Next is the Christian Classics Ethereal Library. This is a collection of multiple writings from Christian history, including works of theology, spirituality, philosophy, commentaries, and on it goes. They're constantly adding new texts. Some of it, like the writings of the Church Fathers, is available elsewhere, such as the Catholic Encyclopedia. But CCEL is the best one-stop shop for Christian writings through the ages.
I added Early Modern Philosophy to the list a few months ago. It's fairly limited, focusing on a handful of the most important authors and texts, but it's still helpful. Run by the philosopher Jonathan Bennett.
EpistemeLinks is a linkwell to philosophy sites. It's not a collection of writings itself, but links to other sites that focus on particular authors or subjects, including texts of many works throughout philosophical history. Very valuable.
Internet Classics Archive does the same thing as CCEL, but instead of collecting specifically Christian writings it collects the writings of ancient authors, whether they be plays, poetry, political commentary, history, philosophy, or theology. Also very valuable.
Islamic Philosophy Online collects many of the most important writings of Muslim philosophers and commentary on them, as well as contemporary writings (like this one). If you look up particular Muslim philosophers on EpistemeLinks, many of the links go to this site. Islamic philosophy is something of particular interest to me, and it doesn't seem to me to get the attention it deserves in the West, to our detriment.
Stanford Encyclopedia of Philosophy is an excellent collection of in-depth articles on philosophical topics. It's an ongoing project, which means there are plenty of gaps where important topics do not yet have their own entry. But it's incredibly extensive on the subjects it addresses, and worth spending a lot of time on.
Finally, I'm including Wikipedia (that's English; it's available in many other languages as well) because it's the most extensive online encyclopedia of everything. Often, I'll link to it on a general subject, even though it has pretty daunting weaknesses. In my experience it's reliable, although when the subject is politics, the people who write the entries are constantly trying to "silence" their opponents. Other than that, though, it's helpful.
Update (3 Sep 2009): I've added a few more links; see here.