Theme Test Drive
Theme Test Drive WordPress plugin allows you to safely test drive any theme on your blog as administrator, while visitors still use the default one. It happens completely transparent and they will not even notice you run a different theme for yourself.
Best part is you can even set the testing theme options (if it has them) in the Admin panel while you are testing the theme.
Development Theme Test
Trying to edit your theme or test a new theme can be very difficult without a testing server or a dev location. Dev Theme Test allows you to create a password protected and non-password protected subdomain such as dev.yoursite.com in order to make modifications to your current theme or a new theme while still displaying your original theme to site visitors. Test drive your themes and use our theme tester!