The Chicago Manual of Style Online
Online version of the classic editing/grammar/writing manual.
#reference
HTML Dog
“HTML and CSS Tutorials, References, and Articles”
Atom Landscape Overview
Excellent list of resources/links/specs relating to Atom and AtomPub.
URL Shorteners
A comparison matrix between a bunch of the more popular URL shortening services.
WordPress hooks database
“his WordPress hooks database automatically scans each WP build for apply_filters() and do_action() to figure out exactly which hooks are available in each version and where the hooks occur.”
Hidden Features of PHP?
Awesome list of “hidden” features in PHP on StackOverflow. Really good collection of tips, pointers etc.
URL Shorteners
Massive collection of screenshots from URL shortening services, collected by Chris Messina
Entity Code
“A Clear and Quick Reference to HTML Entities Codes”
GreaseSpot
The documentation wiki for Greasemonkey. Lots of greasy monkey goodness.
The Ultimate Website Launch Checklist
The Ultimate Website Launch Checklist
Nice list (available in PDF) to go through and check things off when launching a site.