An essential source of information for all things web - from designers to developers, front-end and back.
A blog from Thomas Fuchs, the author of Zepto.js and script.aculo.us.
A very interesting blog from the "Principal Developer Evangelist of the Mozilla Developer Network"
Up-to-date reports on browser compatibilities and any weird implementations that you might need to keep an eye on.
This is so useful that I would marry it if I could...
Ultimate CSS Gradient Generator
...but I would cheat on the above with this nifty tool in a heartbeat.