Top companies for security analysis of a website?

I want to get a asp.net web application audited. A simple google is not giving me the information I am looking for. Has anyone had to perform security audit/scan of their web app? If yes, which company do you recommand also which to avoid? My goal is two folds: to improve the security profile of the app, also use it for marketing - highlighting ...this site has been reviewed for security and privacy by xxxx company. We do not store PII or PHI...so it does not have to be too deep. Thanks in advance. D