The popular skinning app for jailbroken iPhones, DreamBoard, is now free on Cydia. DreamBoard is a great alternative to Winterboard because it doesn't require you to restart your springboard every time you change themes. Dreamboard also allows much "deeper" themes and user-interface redesigns compared to Winterboard. Where Winterboard basically allows theme developers to re-skin existing iPhone graphics and interfaces, Dreamboard allows theme developers to build entirely new interfaces and methods of displaying information.
The free jailbreak app allows you to add a variety of themes to your iOS device, including an Android type theme that places a calendar widget at the top of your home screen.
The most recent edition of DreamBoard comes with support for lockscreens and improved keyboard access. DreamBoard previously sold for $2.99 in the Cydia app store.