Zammy-Sam said:versiontracker.com is so easy to use. Simply search for "merge mp3" and you get this:
http://www.versiontracker.com/dyn/moreinfo/macosx/20670
Enjoy!
scruffy said:this might help:
http://mpgedit.org
From their docs, they offer this example usage:
mpgedit -o output.mp3 -e- test1_1.mp3 test1_2.mp3 test1_3.mp3 test1_4.mp3
Which is supposed to make one mp3 file out of the four test1_[1-4].mp3 files.