ClusterMonkey.net - Learning About Clusters Page
Many good links including: Robert Brown's Getting Started With Clusters, ClusterMonkey's Links Page, Best of The Beowulf List, On-going Cluster Projects, Cluster Opinions

NASA: Beowulf History
In the summer of 1994 Thomas Sterling and Don Becker, working at CESDIS under the sponsorship of the ESS project, built a cluster computer consisting of 16 DX4 processors connected by channel bonded Ethernet. They called their machine Beowulf. The machine was an instant success and their idea of providing COTS (Commodity off the shelf) base systems to satisfy specific computational requirements quickly spread through NASA and into the academic and research communities. ...

LinuxGeek.com: What is Clustering?
Linux has a large selection of clustering systems available for different uses and needs. That doesn't make it any easier for those trying to figure out what clustering system they should use.

User Groups

BWBUG (Baltimore-Washington Beowulf Users Group)
http://www.bwbug.org

BWBUG is a User Group supporting Open Source Computing Systems, mainly those used for high performance computing and Linux used in the Enterprise for applications like Database and Data Mining. We meet monthly.

Gelato.org
http://www.gelato.org
The Gelato portal is dedicated to providing the IA-64 Linux community with the most current and useful resources for running Linux on the Itanium (IA-64) platform.