Rijk's panelizer

The "Add panel" button adds an entry to Opera 12's or Firefox's bookmarks or Mozilla/Seamonkey's panels list. The page will be directly available as a panel in Opera's "Panels" (F4) or Mozilla's/Seamonkey's "Sidebar" (F9). In the case of Firefox, open the page in the "Sidebar" by selecting it from the Bookmarks.

Opera 15 will not support panels, and neither do Chrome, Safari or IE, so for those browsers you are better off with my standalone Quick Reference pages for HTML, CSS and HTTP/1.1.

Preview

Panels linked to online content or services

Add panel Preview HTML Quick Reference
Navigate the elements and attributes HTML with ease! Links to the spec on www.whatwg.org.
Add panel Preview CSS Quick Reference
Navigate the properties, values, and contents of CSS (2.1 and later) with ease! Links to the specs on www.w3.org.
Add panel Preview JavaScript Guide
Index for the JavaScript Guide on Mozilla Developer Network
Add panel Preview HTTP/1.1 cheatsheet
Modified from Hallvord's cheatsheet for the HTTP/1.1 specification, extended by Michael Johnson with extra response codes, method headers, and links to the RFC.
Add panel Preview Lipsum
Generate Lorem Ipsum text, using the Lorem generator from http://www.lipsum.com
Add panel Preview ROT 13
Decode/Encode ROT 13
Add panel Preview Ascii-Hex convertor
Convert ASCII to hex and vice versa
Add panel Preview Stopwatch
Simple JavaScript stopwatch

Panels hosted at third party sites

Add panel Preview Python
With links to Python documentation, from Edgewall.org
Add panel Preview Unicode Charts
All Unicode Charts, in a pretty layout, by Aleto
Add panel Preview HTML Entities
HTML entity reference, from Toman.
Add panel Preview PHP Function Reference
With links to the PHP manual, from Toman
Add panel Preview Colors
Color reference for HTML/CSS, with name and hex code, from Toman.

Mobile Sites

Add panel Google Calendar
Mobile version of Google Calendar
Add panel Google Reader
Mobile version of Google Reader
Add panel Twitter Mobile
Mobile version of Twitter

Style settings

Choose the link colors for this page and the panels styled the same way: