Joomla!® 2.5 is set to be released on the 24th of January 2012.
This release will be a Long Term Support (LTS) release, and will be supported for at least 18 months.
In April 2012 Joomla! 1.5 will reach end of life (EOL), and thereafterr that edtition of Joomla! will no longer be supported. We therefore recommend that you start to plan migrating your 1.5.x web site to the latest version, namely Joomla! 2.5.
If you would like to try out the new version, you can download Joomla! 2.5 Beta. Please note that you should not use this Beta version on a production site!