NetworkX (NX) is a Python package for the creation, manipulation, and 
study of the structure, dynamics, and functions of complex networks.
Features:
* Includes standard graph-theoretic and statistical physics functions
* Easy exchange of network algorithms between applications, disciplines, 
  and platforms
* Includes many classic graphs and synthetic networks
* Nodes and edges can be "anything" (e.g. time-series, text, images, 
  XML records)
* Exploits existing code from high-quality legacy software in C, C++, 
  Fortran, etc.
* Open source (encourages community input)
* Unit-tested

Additional benefits due to Python:
* Allows fast prototyping of new algorithms
* Easy to teach
* Multi-platform
* Allows easy access to almost any database

WWW: http://networkx.lanl.gov