Rominator lets you organize all of your DS roms with ease, view their information, trim them, or even transfer your legally backed up games straight onto your backup cart.
It is cross-platform, and the OS X version also allows Rom icon/header/game code/title editing, and also rom trimming (using safe-trim).
Transferring files is as easy as drag'n'drop and also allows backup of your DS savegames when you plug your card into the mac.

It is a Donationware program for members of GBAtemp.net (free to join).