StayPressed is a free WordPress theme, with a double-column right hand-sidebar and a magazine style – kept simple, to let your blog content do the talking
Case is a dark WordPress theme with blue accents. It has an Ajax box in the sidebar that allows you to switch between categories, tags, recent comments, and recent posts without reloading the page and without taking up a lot of space, which keeps your blog nice and clean.
Iris is a a two column WordPress theme with Iris like colors. The theme is mostly purple, with pink, and blue, with nice gradients and textures. It has nice rounded corners on every post to separate them and drive focus to the content. It is widget ready and ready to demo and download.
Two column, black and white theme
Two column gravatar and widget ready theme with ability to post images directly to the frontpage
Three columns autumn theme with simple illustration for the header and maple leaf icon for the sidebar title.
Three column blue and white theme with a right and left sidebar
Ships Ahoy is three column, widget-ready theme.
With the impending release of WordPress 2.7, Otto has written a very nice article explaining how to get a theme ready for 2.7 to take care of the comments enhancements.