As mentioned on the official PHP.net site today, the latest version of the PHP 5.5.x series has been released - PHP 5.5.5:
The PHP development team announces the immediate availability of PHP 5.5.5. This release fixes about twenty bugs against PHP 5.5.4, some of them regarding the build system. All PHP users are encouraged to upgrade to this new version.
You can download it from all of the usual sources - the source from the main downloads page or the Windows binaries from windows.php.net. If you're interested in what changed in this release, check out the full Changelog. The release includes fixes in the CLI server, Datetime functionality, filtering, sockets and the XMLReader (among several others).