Joomla!® 2.5.6 is now available for download.
This release is the latest in the 2.5 series, and includes updates and fixes.
If you are still using Joomla! 1.5 you should have a look at all the new features that's available in 2.5
Official support for the 1.5 series is said to end later this year, and it would be a good idea to start making plans to upgrade to the latest Long Term Support version (2.5)
Those who are still on 1.6.x or 1.7.x are strongly encouraged to Update to 2.5 without delay, since none the 1.6 and 1.7 series are no longer supported, and not secure.
Further new features, that many will appreciate, were also added since 2.5.5