So you make a living developing themes and plugins for the WordPress community? You will need to set up demo sites for your scripts if you would like to make more sales. Plugin Demo is just the plugin for the job. It lets you create demo sites for your scripts, so those interested can try them before downloading or buying.
Plugin Demo lets you customize the login page, including logo, text, and other settings. Simply select the product you want to demonstrate, choose demo user, select custom post type your plugin creates, and the rest is easy. Cleaning data can be done on a frequent basis to keep your site functioning even after your customers play with it.
This is a paid plugin by pvw. More info is available here.