Athens Neutron Monitor - Observing cosmic ray neutrons. Background information, explanation of worldwide monitor network, detector description, publications, links.
CHICOS - California HIgh school Cosmic ray ObServatory - An active research array for the detection of ultra-high energy cosmic rays. The events CHICOS is designed to observe are single subatomic particles slamming into the Earth's atmosphere with the energy of a brick falling from a rooftop. It is a collaboration of Los Angeles-area high schools, California Institute of Technology, California State University, Northridge, and University of California, Irvine.
Homebrew Cosmic Ray Muon Detector - Schematics and diagrams for the Geiger-Mueller detectors and electronics. Information on cosmic rays, variations and other forms of detection such as scintillation.
ICRR - Institute for Cosmic Ray Research, University of Tokyo.