Building Scalable Web Sites
The Art of Capacity Planning
The Art of Scalability http://www.amazon.com/Art-Scalability-Architecture-Organizat...
Scalable Internet Architectures http://www.amazon.com/Scalable-Internet-Architectures-Theo-S...
Enterprise Cloud Computing http://www.amazon.com/Enterprise-Cloud-Computing-Architectur...
And if you're in doubt, John is now VP of Ops at Etsy and came from Flickr before that:
His blog is interesting too:
So without having read the books, I would shoot for the latter 2 if I wanted to have hard copies around to introduce me to this kind of stuff.