I saw that you have already some right here on this site, and the others gave recommendations for more.
You could also put testimonials on your website where the issue of registration does not exist. I recently had a wonderful comment from a participants in my class, and I asked her whether I could put this on my website. She was happy to agree to it. There you can ask the person how they want their name to appear. Not everybody wants to have a ‘web presence’.