Dean Leffingwell, previously known for his book Managing Software Requirements: a Use-case driven approach has just published a new book entitled Scaling Software Agility: Best-Practices for Large Enterprises. He also has a corresponding Scaling Software Agility blog. See the forthcoming reviews on amazon.com.
So how did Dean go from being a requirements-management guru to being a large-scale agile guru? It's not too big of a leap if you think about it! Dean is at Rally Software Development these days (the noted Agile consulting services & tool vendor) and has also authored a few Agile Whitepapers, an essay on The Essence of Agile (now an excerpt from the book), and a few articles for The Agile Journal, most notably Agile at Scale: 7+7 Practices for Enterprise Agility.