VideoLan says it will soon release a major 2.0 release of its open source VLC media player, which will contain many new features of interest to OS X users.
The new VLC will support Blu-ray playback, if you have the proper hardware, a full screen mode in Lion, and a new interface that looks similar to iTunes.
The 2.0 version is currently available as a release candidate, but it may, of course, still have some unsquashed bugs.
Steve Jobs was famously against building Blu-ray support into the Mac, calling licensing issues a “bag of hurt.” The Mac does support internal and external Blu-ray drives for data storage. With the VLC software, those drives should be able to play Blu-ray movies.
There have been some 3rd party Blu-ray software solutions, but this will be free, and we hope, reliable.