I used to use NcFTPd for the longest time, on various flavors of UNIX. But I got frustrated, I think because either the lack of monitoring tools or that they didn't work right under OS X, and due to lack of usage on OS X, Mike Gleason seems to have no interest in fixing them. So after some research I went to PureFTPd. It's free and has awesome options for user management and server monitoring. I highly recommend it.