WordPress’s themes are absolutly amazing, except you are not able to theme the login pages very well. Smithers Login is a light weight plugin that will allow you full theme control over the WordPress Multisite login pages. This plugin allows for different custom login screens on a single WordPress 3.0 Multisite with Domain Mapping. This Network Activated plugin enables you to specify a stylesheet to be used with every multisite login page allowing for custom login images and messages.
Some Features: