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.
UsabilityTools - Where UX meets Conversion. Unlock the Potential Behind Remote Research and Testing
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.
Feedjit - Feedjit lets you see friends and visitors as they arrive on your blog or website.
idea.informer - Idea Informer is a idea forum similar to uservoice or getsatisfaction.
Invision - Prototyping and collaboration for design teams