What is the normal fan speed for the 15'' Retina Macbook Pro?
I've been monitoring my fan speeds for as long as I've had my device. At idle, the lowest it gets is hovering around 2000rpm. The left fan is usually closer to 2100rpm, actually. The maximum speed appears to be 6000rpm, which occurs during gaming and heavy CPU loads.

SMC Fan Control lets you monitor and control your fan speeds. The minimum setting is 2000rpm and the max is 6000rpm, so I think we can safely conclude that these are the standard maximum and minimum values.