I would make to make a small WYSIWYG editor similar to the one used by StackOverflow. Basically, it would have buttons like [quote], and when that button is clicked, [quote] [/quote] should be inserted in the textarea where the cursor is or at the end of all other text. If the [quote][/quote] could be highlighted in some way that would be even more excellent, but its not required.
Is there any WYSIWYG editor already available where you can add custom buttons, with custom text being added to the textbox as a result?