Wikiwand - A beautiful new interface to Wikipedia
Stylebot - Change the appearance of websites instantly. Preview and install styles created by other users on stylebot.me
FreeStylerWs - Styles and skins for all popular sites in the web
Amino Editor - Amino is a Chrome browser extension for customizing web page presentation with user CSS.
Stylus - EXPRESSIVE, DYNAMIC, ROBUST CSS
Navi Live CSS Editor - Navi Live CSS Editor lets you write CSS code and view the changes simultaneously.