The latest version of Mesa can be downloaded from Softpedia
Mesa, an open source implementation of the OpenGL specification and a system for rendering interactive 3D graphics, is now at version 9.2 RC1.Mesa 9.2 RC1 is the next iteration in the series and it implements the OpenGL 3.1 API. This means that some drivers might not support the specification for the latest Mesa.
According to the developers, quite a few new features have been implemented, including GL_ARB_texture_storage on radeon, r200, and nouveau, a new freedreno gallium driver, an OSMesa interface for gallium llvmpipe/softpipe drivers, and much more.
A complete list of updates and changes can be found in the official changelog, which is inside the archive.
Download Mesa 9.2 RC1 right now from Softpedia. Remember that this is a development version and it should NOT be installed on production machines. It is intended for testing purposes only.