There is a good reference there:
http://www.blogwriteforceos.com/blogwrite/fortune_500_blogs/. Debbie Weil has made a great job referencing who is doing what. She is writing a book about corporate blogging: http://blogwrite.blogs.com/book/
I have discovered HP blog usage through this. HP Blogs are there:
http://h71028.www7.hp.com/enterprise/cache/104417-0-0-225-121.aspx