The simply the best collection of textarea scripts
JEIP is a jQuery plugin to enable editing in place for input, textarea and select elements.
A plugin to automatically adjust textarea height.
A JavaScript jQuery plugin turns any textarea into a markup editor. Html, Textile, Wiki syntax, Markdown, BBcode or your own markup system can be implemented.
Emmet plugin to create a code editor in a HTML textarea.
A platform independent Javascript HTML WYSIWYG editor released as Open Source under LGPL. TinyMCE has the ability to convert HTML textarea fields or other HTML elements to editor instances. Also available as jQuery plugin.