Tantric has released libwiigui 1.03 :

libwiigui is a GPL licensed GUI library for the Wii, created to help structure the design of a complicated GUI interface, and to enable an author to create a sophisticated, feature-rich GUI. It was originally conceived and written after I started to design a GUI for Snes9x GX, and found libwiisprite and GRRLIB inadequate for the purpose. It uses GX for drawing, and makes use of PNGU for displaying images and FreeTypeGX for text. It was designed to be flexible and is easy to modify - don't be afraid to change the way it works or expand it to suit your GUI's purposes! If you do, and you think your changes might benefit others, please share them so they might be added to the project!

Features
Extensible classes
Built-in TTF, PNG support (uses FreeTypeGX and PNGU/libpng)
Built-in sound support (OGG and PCM)
Integrated hotspot support
Automatic handling of navigation via controller pad
Window focus support
Sophisticated object positioning
Comprehensive object state and event system
Support for animated effects
Included template and sample class extensions (eg: on-screen keyboard)

1.03 - May 22, 2009
Add file browser class to template - browses your SD card
New images for the template (thanks mvit!)
Add a function to get the parent element

http://code.google.com/p/libwiigui/downloads/list