Delta Airlines has a blog, Under The Wing, launched in August of 2007, and their blog was not listed on the Fortune 500 business blogging wiki. The Delta blog pushes the number of corporate blogs in the Fortune 500 up to 54 or 10.8%.
Thanks to Jeremy Wright and his article on Fortune 500 companies with corporate blogs in 2005. Though many of the companies Jeremy listed were not on the list of Fortune 500 companies with corporate blogs, I could only find Delta's blog as a new addition. I'd be interested to hear more about the other companies' use of social media.
The blog is a good candidate for a review by a blogger on their blog.