I have the LG HL-DT-ST BD-RE WH14NS40 (from my Mac Pro system report) from MacSales (OWC), aka
Quantity: 1 LGEWH14NS40, $97.99 each
LG 14X Blu-ray Burner + Super-MultiDrive DVD/DVD DL/CDRW Reader & Writer
It works fine in ML, does not "disappear," nor click every few minutes as some have reported. I had purchased a Pioneer BDR-207, but it would hang my OSX 10.7 system when it went to sleep, after I used Toast, etc. I don't recommend that one.
I got the demo BluRay player: MacGo Mac Blu-Ray Player (
http://www.macblurayplayer.com), and it works well enough, though the decoding of commercial BRD is a bit blocky (maybe interlacing artifacts, who knows, but the same BRDs work great in my Pioneer BDP-05FD and Playstation 3. But what you don't get is all the clever BluRay menus, pop ups, etc. Not even the chapter names. So it's OK to see if what you've burned in Toast look adequate, but it is NOT a regulation BluRay player that you might expect. I don't think such a beast exists for Mac.