Inline Comments with Images, Quicktags and Live Preview
Advanced - there is no detailed how-to for this hack, although there are instructions for each element.
This is a combination of three interrelated webpage modifications, Browservulsel's custom comments, Alex King's Quicktags and Scripty Goddess's live preview. The end result is an inline comment submission form that allows for the addition of basic HTML formatting with one click, as well as including images of commenters, and a "live preview" of the comment.
Install each of these three comment modification tools in turn.