Ilia Alshanetsky has announced the release of the latest Release Candidate in the PHP 5.2.1 series - PHP 5.2.1RC4:
I've packaged what looks the be the final RC for the 5.2.1 release, RC4. This release fixes another dozen or so bugs since the last release and from the given feedback looks to be regression free. That said I'd like to ask everyone to take a few minutes and try this RC with their code to make sure it really is as good as it seems and to ensure no new issues are introduced.
So, give it one last run through and submit any problems you might have and get us to PHP 5.2.1 that much sooner.