I have an LG Blu-Ray drive in my 2006 Mac Pro, connected using one of the ODD SATA ports located behind the front fan assembly. It used to be external, but the enclosure died and it now works just fine as an internal drive.
Basically any modern 5.25" SATA Blu-Ray drive will work. You'll need a SATA cable to connect it to one of the ODD SATA ports, and a molex to SATA power cable if the drive doesn't have a molex power input.