Does anyone know of any detailed architectural design patterns for organizing a web application with multiple servlets (and optionally, JSPs)?
You can consider the "MVC Design Pattern", a.k.a. "Model 2 Architecture".
There is an interesting article on Javaworld: Understanding JavaServer Pages Model 2 architecture. In addition, you can take a look at Struts, one of the many projects of the Apache foundation regarding Java. [ Ross Keatinge adds:
Also check out Webwork which is an MVC framework similar to Struts. For me as a Java newbie it was a lot easier to understand and get started with than Struts. ]