AG In Place Editor is a small(3 kb min) jquery plugin for editing any content in-place and saving it with AJAX.
Some ideas and apperance taken from SilverIPE (http://www.silverscripting.com - link seems dead)
- Save on blur (on by default)
- Any inline or block element can be made editable
- callbacks for save and cancel editing
- can be used with an empty url (for callback only)