I needed to make a USB bootable drive of pfSense and being an OS X newb, had to Google it. Here’s what I found. Run these commands from Terminal.

Find your USB drive in the list, mine was /dev/disk2. Unmount the drive if it is currently mounted, umount /dev/disk2

Now, there’s two commands you can run, dd with /rdisk2 gave me 15.33 KB/s. dd with just /disk2 only gave me 4.60 KB/s.

Change input file and output file as necessary. If /dev/rdisk does not work for some reason just use of=/dev/disk2

When using rdisk2 my flash drive was constantly flashing with activity, with just disk2 it would flash for a few seconds followed by a few minutes of no activity. Use /dev/rdiskN where N is your USB drive.