95% of the information on the web is written language. It is only logical to say that a web designer should get good training in the main discipline of shaping written information, in other words: Typography.

Oliver Reichenstein, 2006

Ellen Lupton—Thinking With Type
An excellent book to buy

“Foundries, tools and web font services often group typefaces by use, too—like “intended size” at Webtype and the paragraph and heading buttons at Typekit. And once in a while you can find a nice feature, article or blog post about fonts for specific uses, like the good for long form Typekit list, or Billy Whited’s posts on setting type for user interfaces.”
Lecture/Discussion: What is good digital design?

Typographic Design Patterns And Current Practices (2013 Edition)

The Elements of Typographic Style Applied to the Web: 
A Practical Guide to Web Typography, Richard Rutter

typotheque.com article on type hinting
Hinting, or screen optimising, is the process by which TrueType or PostScript fonts are adjusted for maximum readability on computer monitors. This text compares different ways of hinting (black & white, grey-scale, ClearType, DirectWrite), and explains the behaviour of fonts under different rasterisers.

Some interesting places to look at website hierarchy and digital type:
The Great Discontent uses Stratum and Meta Serif Web Pro
fonts for a dynamic yet respectable feel.
An Event Apart demonstrates the readability of a subdued color scheme.
Vice News
New York Times
The Guardian
The New Yorker
The Webby Awards

More on digital type:
Jason Pamental interview
HWdesignco doing digital right
Khoi Vinh grids are good