Edward Tufte's books, I find that these are the best books on data graphics.
Vischeck.com. Test Web pages for color blindness issues.
Discussion of OpenType fonts.
Type & Layout, by Colin Weildon. Studies of the effects of typography on reading comprehension.
The Elements of Typographic Style, by Robert Bringhurst. My favorite book on typography.
webtypography.net The Elements of Typographic Style applied to the Web.
Dave Thompson's color palette.
Spacing at End of Sentence
Use a single space at the end of a sentence and after a colon. Double spaces date back to the days of typewriters, when all characters were allotted the same amount of space. Computerized typesetting adjusts the spacing for a good fit. Extra spaces create gaps and look unprofessional.