UserVoice - UserVoice integrates easy-to-use feedback, helpdesk, and knowledge base management tools in one platform that empowers users to speak and companies to understand.
Survicate - Collect feedback on your website and find out more about your visitors.
FEEDBACKdeck - FEEDBACKdeck brings to WordPress, a gorgeous way to capture user feedback.
Survey Monkey - Create and publish online surveys in minutes, and view results graphically and in real time. SurveyMonkey provides free online questionnaire and survey software.
SurveyJS - Feature rich and open source surveys for embedding into websites.
FeedBear - The smartest way to manage feedback from your customers