The PHP.net site has officially announced the availability of the latest Release Candidate for the PHP 5.4.x series - PHP 5.4 RC2:

The PHP development team is proud to announce the second release candidate of PHP 5.4. PHP 5.4 includes new language features and removes several legacy (deprecated) behaviours. Windows binaries can be downloaded from the Windows QA site. THIS IS A RELEASE CANDIDATE - DO NOT USE IT IN PRODUCTION!. This is the second release candidate. The release candidate phase is intended as a period of bug fixing prior to the stable release. No new features should be included before the final version of PHP 5.4.0.

Fixes in this new version include updates to the built-in web server, PHP-FPM no longer being marked as experimental and changes to the Zend Engine, Core and various extensions. See the NEWS file for complete details. You can download this latest release from the downloads page (and here for Windows users).