Drupal 7 - Give permission to manage users but not permissions
I had the exact same requirement, and I was able to use the Roles Delegation module to build it to perfection :-)

Here is my scenario to give you more context - 


I had a drupal site with roles - A, B, C, Admin, Maint
I wanted users with role Maint to be able to create new users and also assign them roles while doing so
I also wanted to limit Maint users to be able to assign only roles A, B, C to the new users and not the role Admin
All of it was just a few clicks with the Roles Delegation module


Hope this helps.