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.
FEEDBACKdeck - FEEDBACKdeck brings to WordPress, a gorgeous way to capture user feedback.
GetSatisfaction - Get Satisfaction is the leading customer engagement platform that helps companies build better relationships with their customers and prospects, through the best online customer community.
Survicate - Collect feedback on your website and find out more about your visitors.
idea.informer - Idea Informer is a idea forum similar to uservoice or getsatisfaction.
FeedBear - The smartest way to manage feedback from your customers