The Social Mapping Framework
SocMap draws maps of communities on Twitter, starting from seed users you specify, then expanding to anyone they mention or retweet, then anyone they mention and retweet, ...
The results can be viewed in graphing software like Gephi or Cytoscape to produce graphs like the following:
See map examples for more.
Run ./socmap.py --help for usage, or see the full web documentation for more details.