My Mac doesn't recognize my Galaxy S2 through USB
tested on mac osx snow leopard and Mountain Lion:
with your device unplugged go to settings->developer options disable usb debugging;

Go to Settings, in wireless and network section, go to "more"->usb utilities Tap on "Connect storage to PC". Plug in your device to your mac and the tap on "Turn on USB storage" and OK. You should see your device just like an USB pen.