Interesting critique of the Analysis of Competing Hypotheses method, by Tim van Gelder (of the Rationale tool, and some famous anti-representationalist arguments). Worth a good scan.
Social Network Analysis: A Handbook
The famous 'blue book' primer. Start here.
Models and Methods in Social Network Analysis (Structural Analysis in the Social Sciences)
Excellent collection of more advanced papers.
Social Networks and Organizations
More of an organisational focus than others on this list. Readable.
Not SNA, but still worth study.
Theories of Communication Networks
Very readable modern companion to Wasserman et al.
Sensemaking in Organizations
The place to start, for sensemaking.
The Social Life of Information
Readable, quotable, political work on IT.
Six Degrees: The New Science of Networks
A popular book with depth.