Web Editor Online

http://dabblet.com/
http://codepen.io/

RealTime Preview ( Auto Preview ) HTML
http://htmledit.squarefree.com/
http://www.htmlinstant.com/
http://www.timsfreestuff.com/HTMLEditor/
http://gaf210.imvustylez.net/codes/gadgets/html-editor-lang-eng
Hyro
http://jawerty.github.io/Hyro/
A real-time desktop HTML5 editor — view your html while you code it.

SnapEditor – An Online HTML5 WYSIWYG Editor.
http://www.snapeditor.com/live_demos

CSSDesk – Online CSS Sandbox
http://cssdesk.com/

plugnedithttp://plugnedit.com/
Drag And Drop HTML Editor Online WYSIWYG Visual Editor, Free HTML Editor Online Web Page Builder, Web Based WYSIWYG Editor. WYSIWYG (What You See Is What You Get.) Advanced HTML Visual Editor, Just Drag & Drop Your Images And Text Boxes, Click And Move. Plug & Edit is based on a 3D page building design with height, width and depth.

Javalaunchhttp://javalaunch.com/HTML_Editor.jsp
You can edit the text and run the code.

Ref:
http://www.cssauthor.com/best-free-code-editors/
http://www.w3tutz.com/html/20-useful-online-html-editors-for-web-developers.html