Download Raspbian latest, unzip or otherwise extract it. It’s possible to pipe the dd command through scripts that can show you a progress bar, in my experience this causes it to take a LOT longer, so not really worth it in my opinion.
Open a terminal
diskutil list
Which disk is the sd card?
sudo diskutil unmountDisk /dev/disk#
Then copy the file, upon completion your mac will say “finished”…Pro Tip on a mac… Type sudo dd bs=1m if= and then open finder and drag the .img file to the terminal so you don’t have to use effort.
After the if (input file) space, of=dev/rdisk#
add a ;, and then add “say finished” so it will let you know when it’s done, or if/when it errors out.
sudo dd bs=1m if=~/path/to/raspbian.img of=/dev/rdisk#; say finished
Once that’s finished…
Open the /boot directory
edit config.txt
append dtoverlay=dwc2
open terminal, cd /Volumes/boot
touch ssh
Edit cmdline.txt.
After the “rootwait” text, insert modules-load=dwc2,g_ether
Now you will probably want to set up internet connection sharing.
On OS X
Go so system preferences, sharing, click internet sharing (not the tick box) select the tick box for RNDIS, then select the tick box for Internet sharing, it will ask you if your sure, use your best judgement.
Now, you can plug your USB cable into the USB (Closer to the middle, not charging port) of the Pi, and it should boot and you will be able to access it without a monitor via ssh.
You will probably also want to enable internet sharing from your computer to allow the pi to access internet.
Updated 10.1.2017
-Added download instructions and additional info for writing the SD card from a Mac.