I recently had an opportunity to calibrate a Sony professional OLED display. The new PVM-A250 is a wonder to behold. After a few simple adjustments I was able to obtain a reference Rec. 709 image. The image quality this produced was far superior to a two year old FSI LCD monitor that was in the same room.
This product has blacks that essentially go to zero. This is done while maintaining amazing color linearity. The near black grays were also very charcoal with no hint of color or any lack of smoothness from a lack of bit depth.
The off-axis performance of this monitor is also exceptional.
If you are looking for a color grading monitor I would give strong consideration to the TRIMASTER EL line from Sony.