In addition to the MSBuild documentation on MSDN and the MSBuild team blog, there is an MSBuild wiki on Channel9. I had seen it before, but forgotten about it until I saw it mentioned in one of Chris Sells' old blog posts (My First MsBuild Task).
Here's the current table of contents for the wiki.
Frequently Asked Questions General Project File Format Shipping Tasks Loggers Tasks VS / MSBuild Integration Conversion MSBuild.exe Command Line Object Model Scenarios Does Microsoft use MSBuild to build its own products? How to execute CS templates from MSBuild? External Links and Resources Quick Start Tutorials Write a simple project Clean my Build Specify which Target to Build First Build All Files in a Directory Build All Files in a Directory Except One Build the Same Sources with Different Options Use Environment Variables in a Build Check whether an Environment Variable has been set Build a Project with Resources Build Incrementally Use the Same Target in Multiple Project Files Tell MSBuild to Ignore Errors in Tasks Extend MSBuild with a New Task Build a Set of Dependant Projects Run a Custom Tool From my Project Specify Several Build Options on the Command Line Use Reserved XML Characters in Project Files Display an Item List Separated with Commas Convert an Item List into a scalar string Reference the Name or Location of the Project File in the Project File How do I do a recursive copy? Batching Examples MSBuild Specifications How the batching algorithm works How to find targets files in a canonical place MSBuild Community Wish List
Frequently Asked Questions