I prefer the plugin that Ipstenu pointed out. (Well, I can't say "prefer" because I haven't tried the one you have, Jeffro. But these buttons don't look as nice as the ones that come with Comment Form Quicktags.)

Comment Form Quicktags is pretty neat -- I only disabled it on my site because I don't get that many comments and I prefer faster downloading pages.

My question is: what plugin do you use for previews?