Why are there vortex generators under the Boeing 737's cockpit windows?
Apparently, they are there to reduce the cockpit noise. From b737.org.uk:


  Notice the 10 small vortex generators above the radome. These reduce the cockpit noise from the windshield by 3dB.


According to this document, the VGs, along with other improvements like damping/insulation changes, window frame improvement and ECS improvements contribute to a total noise reduction of 3 dB (at 35k ft and Mach 0.78). Though their exact impact is unknown, the reason for VGs are there is to reduce cockpit noise.