One of most useful reports is Administrative Security > Administrative users security assignments. It shows you Configuration Manager administrative users with rights, assigned to them.
The only problem with that report, is that it shows you only groups and users you added as directly as Administrative Users. But, for example, if you have NA\JDoe and you want to see what kind of access that guy has and you don't want to enumerate all his groups in AD manually, this report may come handy.
Upload it to your SSRS with Reporting Point role, change DataSource pointing to the one that Config Manager created for you, and enjoy :)