GeoServer 1.6.1
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This release has over 40 patches and improvements since 1.6.0. They include

* Feature type aliases
* Max features support, defined per feature type
* GetFeatureInfo on raster
* Generate PDFs from raster
* UpdateSequence support in WMS and WCS

And many many more. Check out the entire 1.6.x changelog:
http://jira.codehaus.org/secure/IssueNavigator.jspa?reset=true&&fixfor=14070&pid=10311&sorter/field=issuekey&sorter/order=DESC

This release is based off of Geotools 2.4.1.