41. Rules of Thumb
The goal of Rules of Thumb is to find every rule of thumb, aka unwritten codes for how we do something, and gather them in one gigantic database. As of this writing, there are nearly 5000 different rules of thumb in 155 categories ranging from Advertising to Wine. Basically, if you want to get a feel for a subject, or get a ballpark figure for a complicated process or topic, Rules of Thumb is a good place to start.
WorldMapper is a collection of hundreds of world maps, each focusing on a particular topic. For example, you can find maps on land area, disease, religion, income, and more.
WorldCat allows you to search the largest network of library content and services online, tapping into literally hundreds of different libraries from all over the world.
44. Our Documents
At Our Documents, you can explore 100 cornerstone documents of American history, i.e., the Declaration of Independence, the Constitution, the Bill of Rights, and many more.
The Library of Congress is literally the largest library in the world, with millions of books, recordings, photographs, maps and manuscripts in its collections freely available to the public (you might have noticed that the Library of Congress Online Catalog has already been included in this list; the Library of Congress home page is the hub of ALL the content that the Library has to offer).
The Voice of the Shuttle, started in 1994, is one of the largest humanities resources on the Web today. Anything from anthropology to religious studies is covered here.
This is the original (1919) edition with over 11,000 searchable quotations.