Next stable versions of PHP are released – PHP 5.2.2 and PHP 4.4.7. These contain major stability and security enhancements.
The PHP development team would like to announce the immediate availability of PHP 5.2.2 and availability of PHP 4.4.7. These releases are major stability and security enhancements of the 5.x and 4.4.x branches, and all users are strongly encouraged to upgrade to it as soon as possible. Further details about the PHP 5.2.2 release can be found in the release announcement for 5.2.2, the full list of changes is available in the ChangeLog for PHP 5. Details about the PHP 4.4.7 release can be found in the release announcement for 4.4.7, the full list of changes is available in the ChangeLog for PHP 4.
You can see the major updates done in these two versions by going to PHP website. An upgrade guide is also available for upgradation to PHP 5.2 from PHP 5.0 and PHP 5.1.
I love words free and stable :).