Due to popular request and getting a brief moment to do so, I've added the first-draft list of required world objects which we need concept art and 3D models for.  If you're either a concept artist or modeler looking to contribute to the book "Programming an MMORPG in C# with XNA" and Level-Grind Online, the best thing to do is see the below list and get started.

Once you've got artwork completed, create a new thread for it in the appropriate forums and attach it.

See the List of Required Artwork