I just found a free 96 pages eBook available from Eric Nelson about the windows azure platform. Looked through it very quickly and I thought it would be a very good book to learn the overall of Windows Azure, SQL Azure and the software architecture which will be deployed on Azure. You can download it here.
You can also read the book Cloud Computing with Windows Azure Platform by Roger Jennings online from here. Remember this is just the online version, so you cannot download or print this.
To Get the feel of this book, you can buy from the Amazon link below.
Update : Tuesday, 31st May 2011, While going through the online articles to fetch more and more knowledge on Cloud and What other Cloud Services offers as Compared to Windows Azure, also some very fundamental concepts which I have not discussed till now. i.e. SaaS, Paas, IaaS, etc. I cam across an excellent free eBook (Demystifying the Cloud An introduction to Cloud Computing) provided by Janakiram MSV on one of his post.
I must say the way he has the way he presented everything is something very unique in itself. Once you start reading this book, you will get totally engaged into it. You can download it from his blog link: