Bob's O'Reilly book Learning SPARQL
Bob's blog and some entries about SKOS
W3C list of SKOS datasets (AGROVOC, New York Times, etc.)
Article by Bob on IBM developerWorks Improve your taxonomy management using the W3C SKOS standard
TopQuadrant blog entry How to extend an ontology (using SKOS as example of ontology to extend)
SKOS tools:
TopQuadrant's Enterprise Vocabulary Net
SKOSed Protégé plugin
iQvoc: German home page, GitHub home page (scroll down for readme info in English)