Starting with IIS 7, you can also manage users using IIS.
If you want to do it on-line, you'll need to create your own admin pages that use the Membership API. For example, you can call Membership.GetAllUsers to get a list of all existing users. Not really easy to write, but certainly doable.
There's an article on the MSDN site that describes this: http://msdn.microsoft.com/en-us/library/aa478958.aspx
Also, the chapter Wrox BugBase from my book ASP.NET 2.0 Instant Results has a small management section that shows you how you could accomplish this.