Geokem http://geokem.com/
Online publication with brief descriptions of most types of terrestrial and lunar igneous rocks, their regional distribution and classification, and examples of their geochemical trends and "fingerprints".
Northwest Obsidian Research Lab http://www.obsidianlab.com/
Offers a variety of analytical services related to obsidian trace element characterization ("sourcing") studies, obsidian hydration studies, and obsidian source studies, primarily in the context of archaeological research.
Rob's Granite Page http://uts.cc.utexas.edu/~rmr/
This site is devoted to granite petrology with an emphasis on the Llano Uplift granites of central Texas. Also includes links to research, meetings and other scientists.