Igneous Petrology

Geokem
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".
http://geokem.com/

Greg Finn, Brock University
Page with links to course summaries for Petrology and Petrography, and related coursework.
http://www.brocku.ca/earthsciences/people/gfinn/

Northwest Obsidian Research Lab
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.
http://www.obsidianlab.com/

Pegmatite International
Information on the mineralogy and petrology of pegmatites including an online publication and links to pegmatite-related sites.
http://www.pegmatology.com/

Rob's Granite Page
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.
http://uts.cc.utexas.edu/~rmr/