Ask HN: Recommend a book on Machine Learning and/or Graph Theory?

Hey HN'ers.

A couple of us are part-way through developing our next app (http://pageradius.com/), and the more we get into it, the deeper we're getting into machine learning and graph theory (including frequent itemsets, association rules, bayesian classification, clustering, and so on).

We've scoured the web for as much info as we can and are making pretty good progress, but really want to get stuck into a solid, well-edited book that explains these concepts clearly - we're really loving these subjects.

Any recommendations?

Thanks!