convert WAV to MP3 on MAC

What free software does this? I used to be able to do it in Itunes, I think.
MAX converts any format to any format.
XLD is another.

What are you trying to achieve? If this is simply to convert so more files will fit on an iPhone/iPod then iTunes will do that automatically to AAC their equivalent to mp3.
iTunes. Just go to options then import preferences and change it to mp3 (aac is a much better choice imo.) Highlight your songs, right click then the option to convert to mp3 should be there. Be sure to change it back to Apple Lossless or AIFF after or ripped CDs will be in the mp3/aac format.