The redoubtable Tom Sterling has added 2 new tomes to his Beowulf trilogy. Beowulf Cluster Computing with Linux looks interesting... http://www-mitpress.mit.edu/catalog/item/default.asp?sid=CFCFA42C-161E-4E07- B6B6-E603B7ECFC62&ttype=2&tid=8681 an early pre-signed copy can be viewed at the DeBUG library in January.