As mentioned on the main PHP.net site, the latest Release Candidate for the PHP 5.4.x series is now available for testing:

This is the 2nd release candidate. The release candidate phase is intended as a period of bug fixing prior to the stable release. The release candidate fixes a critical issue when using the internal classes in multiple threads. A complete list of changes since the last release candidate can be found in the NEWS file.

The source packages can be downloaded from the main QA site and the Windows binary packages from the Windows QA site.