I was looking for a plugin which added quicktags and preview to the comments. Unfortunately I did not find any good quicktags plugin for WP 2, the only one that seemed quite good was WP-CommentPreview.
It does not support WP 2 and so I had to change all the options in the plugin files, since it adds no admin interface, and everything seemed good; the only problem is that it generates invalid xhtml. Here is what W3C validator says:
Error Line 86 column 498: document type does not allow element “div” here; missing one of “object”, “applet”, “map”, “iframe”, “button”, “ins”, “del” start-tag.