CSS: An introduction to CSSLint.
Design: Beautiful and creative invitation card ideas.
EMail: Newsletters actually worth subscribing to.
Hotkeys: Obscure and valuable keyboard shortcuts [win/mac].
iPhone: 20 useful apps for developers and designers.
jQuery: Two great plugins for image sliding and modal windows, Orbit and Reveal.
JSON: A very handy tool for viewing/mapping data coming back from JSON requests.
WordPress: The most downloaded plugins of all time.