Google: Introduction to Distributed System Design
Update: Google added videos on Cluster Computing and MapReduce. There are five lectures: Introduction, MapReduce, Distributed File Systems, Clustering Algorithms, and Graph Algorithms.
Advanced website design depends on deep distributed system design knowledge. Where do you get this knowledge? Try Google. They have a a whole Code for Educators program with tutorials and lectures on AJAX programming, distributed systems, and web security. Looks pretty nice.