If you're planning to teach to beginners, I also would recommend TextWrangler from Bare Bones software.  It doesn't have a lot of bells and whistles but is free, easy to use, and was written specifically for Macs.  Won't confuse new coders and can be considered a gateway editor to introduce them to code editors in general.

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Mark Vega
Programmer/Analyst
University of California, Irvine Libraries - Web Services
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