A list of SNA Software.
For a very comprehensive list look at this Wikipedia page.
The software I prefer:
Visone: webpage: http://visone.info/
A great visual tool for building and analyse smaller sized networks. Use it in workshops.
UCINet: webpage: http://www.analytictech.com/ucinet/
I use it for more complex analysis.
NodeXL: webpage: http://nodexl.codeplex.com/
Use it for analysis of e.g. Twitter.