From my viewpoint as a part-time Macintosh user, trantor
gave you two good examples of
Avantgarde text editors
for the Macintosh.
More conservative Macintosh users will prefer the commercial
BBedit,
its free cousin BBeditLite, Alpha or Pepper. A good overview
on Macintosh editors and their URLs you will find at the
Mac TeX/LaTeX Web Site.
HTH
Hanamaki