I have had a 14" toshiba LCD, as a notebook, and I can honestly say it wasnt the gpu in the card making Doom look bad, it is the lack of pixel changing speed on the display.
As for the Apple 22", I have seen graphic design work, such as photoshop, and it looks...great. Unless its in any ambient light area (like a normal workspace for instance) and then you have to *adjust* the settings, beef them up, like any LCD. The SGI f220 below is possibly the most CAD oriented LCD, just from the fact its Silicon Graphics catering to its super high end user base. I would like to see how it performs.
Plasma sounds more promising as these displays are clear in all lighting conditions.