Henrik has recently posted a list of platforms that will be supported when Oracle's JDK 7 first ships (still planned for late July this year). At a high level, the list is very similar to what Sun used to support : Windows, Linux and Solaris.
While Oracle is committed to delivering the JDK on Mac OS X, no date is yet available for this. On the GlassFish side we're tracking closely the progress made by our fellow colleagues in the JDK team with our Mac users relying on the very fine OpenJDK 7 binaries for MacOS X for the time being.
The entry also mentions other operating systems as well as mostly embedded architectures (ARM, Power) via Java SE Embedded.