Links I like

'Facets of Unity' by A.H. Almaas (one of my favourite enneagram books)
Eli Jaxon-Bear's 'Enneagram of Liberation' book
Conscious TV (great collection of interviews, many about the enneagram)
Comprehensive 'Personality Types'  book by Riso and Hudson 
Popular and Informative Site - The Enneagram Institute
Eckhart Tolle's Website (not about the enneagram but a great teacher)
One of the  better lists of well-known enneagram types
Enneagram & Astrology Site (in German with English videos)