Here is the official site for the latest schemas and some ATML sample files. 
http://standards.ieee.org/downloads/1671/

The Phase 3 demo at AutoTestCon 2010 showed the expanding use of ATML across different test systems.

Here are the ATML files for the Phase 3 demo:
http://grouper.ieee.org/groups/scc20/ATML/Demonstrations/Phase3/