I verified that the settings in Central Admin were disabled so that users could not create their own subsites. However, they are still creating their own subsites. Is there a setting in each site that gives users with Full Control the ability to create subsites which can override Central Admin? When I look at Site and Workspace Creation Permissions for the site collection, only "Manage Hierarchy" is checked. What happens if I uncheck that?
There are two rights that control whether users can create a top-level Web site, subsites, or workspaces: Use Self-Service Site Creation and Create Subsites. See this Technet article for details.
Also permissions are defined at the site collection level. For your case you will have to create a new permission level at the site collection where you don't want users to create subsite. See this blog post for how to do this.
Hope this helps!