Logitec (not to be confused with Logitech) does offer a Blu-Ray drive for the Mac Pro. However, right now I do not believe there is a OS X media player that handles Blu-Ray or HD-DVD.
Cyberlink's Power DVD for Windows works, so you could watch them in Boot Camp (not sure if it works in VMWare or Parallels). Though the lack of HDCP on the video card and the display might mean the quality is cut to 540p instead of 1080p (though not sure about this).
People are also using Windows-based rippers on the discs and then converting them into MP4s for watching with Quicktime, VLC, or MPlayer.