If your control inherits from PortalModuleBase, you will have access to ModuleId and TabModuleId, both of which are a unique ID for the instance of your module, depending on exactly what you mean by unique.

You may have noticed that you can add existing modules onto other pages, add a module to all pages, or copy a reference of a module from a page when you create a new page.  All of these copies will have the same ModuleId (and therefore, technically reference the same information), but they will have different TabModuleId.

So, ModuleId usually refers to the content of the module, while TabModuleId refers to the settings (something customizable per instance without affecting the rest of the modules sharing its content).

Hope that helps,