Currently I'm using:
Monitor
Brightness: 30% (adjust to taste I'm not a fan of it too bright myself)
Contrast: 75% (I don't recommend changing it from default 75% as it quickly destroys colour detail)
Colour->Preset Modes->Custom colour: 100, 93, 100 (R, G, B) (On my specific panel 99, 99, 96 is actually more accurate but colours "pop" more with 100, 93, 100 which seem to work the best without fine tuning over all these monitors I've seen so far).
Others->Monitor Deep Sleep: Disable (Some of these panels can be a bit glitchy about coming out of sleep mode* but disabling deep sleep can have high standby power draw - some seeing as high as 20 watt)
Display->Response Time: Normal (generally the fast setting exhibits inversion artefacts, etc. while not appearing to decrease ghosting, etc. any more than the normal setting to any significant level)
nVidia Control Panel - Display->Adjust desktop colour settings
Gamma: 0.75 - 0.92 (Each monitor seems quite different as to how much black crush you get and how much gamma you need to get a good contrast and natural looking saturation - I recommend using
http://www.lagom.nl/lcd-test/black.php to minimise the compromise with black crush to get the best balance).
Digital vibrance: 50-60% (Personally I avoid this setting as it only moves away from accuracy but some like 60% as it makes the colours look deeper and more saturated - if you just like it looking nice and vibrant for gaming then its worth playing with the setting).
I've avoided ICC profiles personally as while they can work well they've been calibrated against a specific monitor and usually need a bit more experience to make the most of - you may also have issue with getting them to stick with specific games and/or dropping out when exiting a game.
* Removing both the power lead and any DisplayPort and/or HDMI sources connected for about 3 seconds should fix it if it happens. Supposedly A03 onwards have fixes for deep sleep problems according to a Dell engineer's post elsewhere but not sure if it is confirmed.