Just this week I launched a shop for WordPress comment designs at http://commentbits.com. I've come across a lot of people who hate styling the nested comments in their theme, and for good reason. CommentBits is one idea I have for remedying that.
The styles themselves run pretty cheap, $7 each, and a Lifetime Pass is available too, for those in it for the long haul. And of course everything is 100% GPL. Go nuts.
I'm interested in any feedback / thoughts from the group here. This is my first foray into commercial WordPress items, so it's pretty exciting. Granted it's not a theme or anything -- but pretty close, right? :)