Open Source (or inexpensive) editor

Does someone know of a simple editor that can be used as a user front
end to create simple html code to be inserted into a form and
processed by a php script.

The specific place I want to use this is on an admin page for a
templating system that will help a user create simple html like lists,
links, image links, etc. in a gui format to be stored in a database.
It would be nice if the user could insert specific css styles as
attributes, or if the editor could be set to insert specific styles in
a WYSIWYG format.

I want this to be able to work on mac machines, so software using
Active X or other proprietary Windows stuff are out.

Thanks,

--Kenoli