1. CKEditor is very nice and stable, it's also already localized in many languages and it autodetects the browser language to display itself in your language. Check it out: http://ckeditor.com/demo

2. WYMEditor is an editor focused on generating perfectly structured XHTML strict code, to conform to the W3C XHTML specifications and to facilitate further processing by modern applications., on http://www.wymeditor.org

3. YUI library (initially created and still used by Yahoo) it has many modules, including a rich text editor http://yuilibrary.com/yui/docs/editor/

4. Any suggestions?

Interesting others:

http://olivier-m.github.io/minislate/#demo   - interesting how you edit the text and you are still on the page doing so.

http://neilj.github.io/Squire/    - clean and simple

http://alex-d.github.io/Trumbowyg/

http://quilljs.com/examples/   interesting normal mode and full mode

http://hackerwins.github.io/summernote/

http://imperavi.com/redactor/    super clean and professional

http://editor.froala.com/#inline-demo   super clean and powerful

http://demos.dojotoolkit.org/demos/editor/demo.html     really complex and powerful, a little overkill

http://maccman.github.io/wysiwyg/   so simple it hurts :)

http://jhtmlarea.codeplex.com   - rather oldschool

https://code.google.com/p/lwrte/

https://code.google.com/p/wkrte/    based off the one above

https://code.google.com/p/loki-editor/

http://www.upian.com/upiansource/ueditor/en/

http://www.upian.com/upiansource/ueditor/demo/

http://www.upian.com/upiansource/ueditor/demo/custom.html

https://github.com/akzhan/jwysiwyg    see examples here http://akzhan.github.io/jwysiwyg/help/examples/

https://github.com/basecamp/wysihat    made by 37Signals https://signalvnoise.com/posts/1330-introducing-wysihat-an-eventually-better-open-source-wysiwyg-editor

List of others:

https://github.com/cheeaun/mooeditable/wiki/Alternative-Javascript-WYSIWYG-editors