This is a collected list of the sample code for Metal that Apple has published so far. Links are subject to change, and all content is preliminary.
MetalBasic3D: OpenGL ES template ported to Metal (published 2014-06-16) developer.apple.com/library/prerelease/ios/samplecode/MetalBasic3D
How to create a basic textured quad. (published 2014-06-16) developer.apple.com/library/prerelease/ios/samplecode/MetalTexturedQuad
How to stream vertex data between 3 command buffers using one block of memory shared by both the CPU and GPU. (published 2014-06-16) developer.apple.com/library/prerelease/ios/samplecode/MetalVertexStreaming