TFS Build: "Microsoft.WebApplication.targets" was not found.
You receive the following error message as build result:
The imported project "C:\Program Files (x86)\MSBuild\Microsoft\VisualStudio\v10.0\WebApplications\Microsoft.WebApplication.targets" was not found. Confirm that the path in the <Import> declaration is correct, and that the file exists on disk.

Solution
- Install Visual Studio on the build server (make sure to check the "Visual Web Developer" component).
Note: Although it might seem strange to install an IDE on a build server it is required for additonal functionality, e.g. Code Coverage only works with VS Premium or above.
(Thanks to my MVP college Anthony for the solution)