Easy to use
http://twitter.github.com/bootst - Twitter Bootstrap
http://foundation.zurb.com/ - Zurb Foundation
Typography
http://www.google.com/webfonts - Google Web Fonts
https://typekit.com/ - Typekit
http://letteringjs.com/ - LetteringJS
http://www.kernjs.com/ - KernJS
http://www.dailyjs.com/ - DailyJS
http://compass-style.org/ - Compass framework
http://lesscss.org/ - CSS Preprocessor Less