What are these antenna-like protrusions for on an airliner?
They are the various communication and navigation antennas of the aircraft. This figure shows the location of antennas in A320, the type of aircraft in picture.



Source: pprune.org

Some antenna (the ones with *) are optional and the installation varies with customer. The communication antenna location in A320 can be seen in this image.



Image from airbus training course from airbus.altervista.org

And the navigation antenna location in this one:



Image from airbus training course from airbus.altervista.org

The dome (2 in the picture) is the radome for the wi-fi system introduced by Jetblue, dubbed Fly-Fi.



Source: nycaviation.com

So, 


1,3,4 - VHF
2 - Wifi
6 - ELT