I found that the softMMCS utility mentioned elsewhere on this forum to be of great help when calibrating my Dell 2407WFP Rev.A04 and Rev.A03 panels:

http://www.dellcommunity.com/supportforums/board/message?board.id=dim_monitor&thread.id=75957

Unfortunately, the "contrast" setting in this application seems to have no visible effect on the display. However, I did find settings for "black level" (red, green and blue) that allowed me to lower the A04's black level to be more like the A03; The A03 appears to have a higher contrast ratio than the A04 but it sacrifices some of the dark-end of the grey scale to accomplish this. Unless you want to crush your dark greys (dark reds, dark greens and dark blues) even further into black, I recommend you leave these settings at their defaults. I lowered mine because I need my two 2407WFP panels (with different revisions) to match. Also, the "luminance" setting appears to use a different measurement than the "brightness" setting on the front panel of the monitor. Setting the luminance to zero (0) in the application would change the monitor's brightness to 30.

Note: There is no "black level" setting in the Rev.A03 panel which is why I didn't just boost the black level on the A03 to match the A04.

One thing I did try which seemed to have a positive effect with my Rev.A04 was to follow Chris' instructions from the forum link above to "Restore factory defaults", even though in theory my display should've already been using factory defaults since I just recently received this brand new monitor from the factory.