"Pattern-oriented Software Architecture Volume 2: Patterns for Concurrent and Networked Objects" by DougSchmidt, MichaelStal, HansRohnert, and FrankBuschmann. Wiley Series in Software Design Patterns. Chichester: John Wiley & Sons, 2000.
See PatternOrientedSoftwareArchitectureOne for information about volume 1.
Also see ServerPatterns.