Fonts.com‘s Fontology is a GREAT resource for most things typography. It is broken down into 4 Levels: A Typographic Foundation, Practical Typography, Numbers, Signs and Symbols, and Designers and Details. Each of these are then divided into sub-categories.
A Typographic Foundation is then divided into Type History, Type Anatomy, and Type Families. Aside from guides to the various typestyles, there is even a brief description about each letter in our alphabet and the origins of each letter.
Practical Typography is the area that I have personally found most interesting to read through. There are articles on Text Typography, Display Typography, Web Typography, Making Type Choices, and Type and Color. ALL of these sections seems to have great tips, advice, and guidelines for applying typography to various projects and in various mediums.
The Numbers, Signs and Symbols is divided into those categories as well as a Correct Marks section which details the proper symbols for the forward slash verse the fraction sign or the correct symbol for multiplication instead of using the letter x.
Lastly, the Designers and Details is separated into Fine Typography, Type Technology, and Influential Personalities.
All in all, Fontology seems like a good-go to source for quick and organized information which I will definitely be accessing in the future.