How do I see who I have registered to my Google Apps Reseller account

First go to admin.google.com

Next login with your resellers account which should be like username@reseller.domain.com

Once you are logged in, on the right side you will see a link that says reseller tools.  Click that.

At this point it takes you to the customer enrollment page.  To see what you have already registered clicked at the top Customer Registration.