I've got dual monitors running on my Alienware M11x laptop. Dell S2409W through DisplayPort and Philips 241E through HDMI.
Somehow, black looks completely different on the two monitors. The Dell's black looks kind of grayish, whereas the Philips' looks super dark.
I've been messing around with brightness and contrast settings for over an hour, restore factory settings, chose different color profiles and did a calibration on two screens. No real improvement so far.