Create a bootable usb stick from ISO file on Mac OS X

1. Have your bootable .iso image file ready
2. Open the Terminal (in /Applications/Utilities/ or query Terminal in Spotlight).
3. Convert the .iso file to .img using the convert option of hdiutil e.g.,

   hdiutil convert -format UDRW -o ~/path/to/debian.img ~/path/to/debian.iso
   mv ~/path/to/debian.img.dmg ~/path/to/debian.img

   
   Note: OS X tends to put the .dmg ending on the output file automatically.
4. Run

   diskutil list

   to get the current list of devices.
5. Insert your usb stick.
6. Run

   diskutil list

   again and determine the device node assigned to your flash media (e.g. /dev/disk2).
7. Run

   diskutil unmountDisk /dev/diskN

   (Note:replace N with the disk number from the last command; in the previous example, N would be 2).
8. Execute

   sudo dd if=/path/to/debian.img of=/dev/rdiskN bs=1m

   (replace /path/to/debian.img with the path where the image file is located).
   Note:Using /dev/rdisk instead of /dev/disk may be faster.
   If you see the error dd: Invalid number '1m', you are using GNU dd. Use the same command but replace bs=1m with bs=1M
   If you see the error dd: /dev/diskN: Resource busy, make sure the disk is not in use. Start the 'Disk Utility.app' and unmount (don't eject) the drive.
9. Run

   diskutil eject /dev/diskN

   and remove your flash media when the command completes.
10. Restart your Mac and press alt/option key while the Mac is restarting to choose the USB stick.