The Nero AAC Encoder encoder is far superior sound-wise to
libfaac that comes with
ffmpeg, but the encoder is only available for Windows. How can I encode using this encoder on Mac OS X?
Other, even better alternatives are encouraged as well.
If you are set on using Nero's encoder on a mac, you can always use Mac's Bootcamp to run a virtual version of Windows and do the encoding that way. This probably isn't what you want but was just going to give you the option.
There are also a few programs that don't require Bootcamp that will open PC programs. Here are a couple. I think some have a free trial too or are free (but in beta) so you wont have to buy anything right away if you wan't to go this route:
However, FFmpeg now also supports the external encoding library from fdk-aac which is probably ≥