Involves: Selective colouring, fill layers, hue/saturation, colour balance and levels.
Level: Easy (6 steps)
PSD: Under the cut. :D
PLEASE comment at

001. Find a base, crop it, sharpen, do whatever you do usually!
002. Layer, new fill layer, solid colour.
#03082a and set to exclusion, 100%.
003. Now we're onto a hue/saturation layer. (Layer, New Adjustment layer, hue/saturation)
Master: 12
Reds: 7
Yellows: 7
Cyans: 10
Blues: 8
004. Levels layer. (Layer, new adjustment, levels)
Input levels:
45, 1.50, 245
Output levels:
17, 255.
005. Now my friend, colour balance. (layer, new adjustment layer, color balance)
Midtones:
-29, -22, 17
Shadows:
20, 21, -34
006. layer, new adjustment layer, selective colouring.
Reds: 90,20, 100, 6.
Yellows: 100, 0, -100, 0.
Cyans: -100, 0, 0, 100.
Whites: 49, 0, -40, -34
Neutrals: 10, 0, 0, -10
& You're done!
I would love to see what you guys have come up with, surprise me!
PSD: oh, i'm ready for it.
Other Examples: