LimeSurvey is a powerful open source survey system, with statistical analysis. LimeSurvey was formlerly known as PHPSurveyor.
From the Author
LimeSurvey (aka PHPSurveyor) is a leading Open Source Online Survey Tool written in PHP.
LimeSurvey allows you to develop, publish and collect responses to surveys. LimeSurvey includes a wide range of built-in question types, and a range of flexible options.
Your surveys can include branching, your own preferred layout and design (using a templating system), and can provide basic statistical analysis of survey results.
Surveys can be public, or can be strictly controlled through the use of "once-only" tokens for each survey participant.
Authors website: http://www.limesurvey.org