I have had success with TechValidate (9 years) followed by UserEvidence (the past several years). The top talent came from TechValidate after the SurveyMonkey acquisition to launch UserEvidence. For me personally, UserEvidence has allowed me to very quickly identify advocates for opportunities (including qualifying for reviews) and generate content for case studies, slideware and social. It's also very easy to collect authorization to share a customer’s name/quote/logo publicly. I haven't had a lot of experience with backend integration but know they can easily integrate with SFDC and several other platforms. I believe UserEvidence offers pricing options for small and large programs.