The WordPress Twenty Twelve theme is coming out later this year. I've been testing it on my blog and the current version in their git repo seems pretty stable. I downloaded this on Friday the 14th September 2012.
You can download it from their dev repo before the launch later this year but I thought I'd whack a link up to make it easy.
Cloud App link: http://cl.ly/1V0g381O0W0w
WordPress repo: https://github.com/WordPress/WordPress