Matthew Schmidt of the iSocial project at the University of Missouri recently posted a video tutorial to the Sun Immersion Special Interest Group (http://sun-isig.ning.com/) outlining how to create a simple terrain for your Wonderland 0.4 worlds using Blender (http://www.blender.org/).
This tutorial provides a visual explanation of the steps involved in 1.) creating the terrain model in Blender, 2.) exporting the terrain in the correct format for Wonderland and 3.) importing that terrain into Wonderland using the built-in model importer in the Wonderland 0.4 client. Using the techniques outlined in this video, you can quickly and easily create a compelling landscape for your Wonderland worlds.