This is where I go for ballroom shoes http://www.cwdanceshoes.com/  mostly because they are more affordable than most and because  my foot is difficult to fit and they have what works best for me.  Another place people tend to like is www.danceplus.com/  but they are a bit more expensive and don't have shoes wide enough for me.  Proper fitting ballroom shoes suited to whatever style (Standard/Latin/etc) are really key for ballroom - both for dancing well and for keeping the feet from getting ruined - I found it out the hard way when I first started.