Retinize it
The best Photoshop actions for preparing designs for iOS or optimized for Retina-display websites.
Gridwax
A vertical rhythm bookmarklet that displays an adjustable vertical grid on any website.
FontPrep
The missing font generator for Mac OSX
Google Typography
wordpress.org/plugins/google-typography/
A simple plugin that lets you use and customize (in real-time!) any fonts from Google Fonts on your existing WordPress site.
Favic-o-matic
Favic-o-matic generates the favicon, both .ico & .png, and the HTML code needed to make your website looks awesome on every browser and every device.