PiWriter is (Yet another) tool to help you make bootable SD-cards for your RaspberryPi in Mac OS X. But it's not limited to just RaspberryPi. You can use it to copy every bootable .img file to both internal and removable disks.
The Universal DMG works for both PowerPC and Intel systems and runs on all OS versions supporting Cocoa.
PiWriter2 initial release is now available in the download section. It features drag and drop support to detect the SD card. Click the 'Files' link to check it out!
Sadly this application appears to no longer function under Yosemite.