Sometimes the best interface is no interface at all. Compared with other Mac uninstall programs, AppTrap is simplicity itself--and it really does seem to provide the uninstall functionality that Apple "forgot" in OS X.
AppTrap is not actually an app but rather a System Preference pane, which you install and then it runs in the background (and you can set AppTrap to automatically start at log-in). Whenever you drag an application to the Trash, AppTrap will prompt you to delete all the application's related files, including any files installed in that application's cache, library, or application support folders.
As with all uninstallers, your mileage may vary and AppTrap may occasionally miss some files--but for a well-designed piece of freeware with a seamless "interface," AppTrap does an excellent job.