Survey™ is a free web based survey and (data entry) forms toolkit for processing and gathering data. It is an open source webapplication written in ASP.NET and C#.
Web Survey Toolbox : Doing online research has never been easier. You can write surveys online, run a clustering survey, and infinitely customize by adding JSP code. It can generate agile reports from JIRA and Bugzilla hours, and online diagrams.
LimeSurvey is a PHP survey software to create online surveys. Features open/closed surveys, branching, participant administration, quotas, WYSIWYG HTML editor, email invitations & reminders, assessments, basic statistics and more.
Encuestame is a Survey Software specialized in creating online Surveys. But not only Surveys, you will also have the opportunity to get the user opinions in different ways, as well as sharing and collecting information trough social network applications like twitter, facebook or in your own website if you wish.