Several months ago I started to develop a very big mod for my future Minecraft-based custom server and had faced one problem: Minecraft GUI library is really painful to use, especially if you had experience in developing GUI's under other platforms. And, since my mod should use a lot of custom GUI windows, I decided to port a very well-designed Android GUI library for it.
As a result, I've made MineDroid — GUI library that manages resources of my mod and allows me to edit and store windows layouts in XML files. Main concepts of it were taken from Android so people who used to develop android applications, probably will find this library very useful and easy to understand. Anyway I've tried to make some documentation for it and even wrote a quick-start guide
Library can be used as a separate library mod, providing your mods ability to make fancy interfaces
Right now it's on beta-testing: if you'll find any bugs, feel free to report about them on the GitHub bug tracker. I'll do my best to fix bugs as soon as possible.
Please, comment if you find this library useful for you. It will affect how much time I will spend to support the library.
Also, there is a plugin for IntelliJ Idea that will help you to manage your resources: it adds autocompletion for XML layouts and generates R.java file with a class containing links to all your resources.