To have your own city or town show up in the Time preferences panel, for selecting your time zone, simply create a symbolic link in the correct /etc/timezones/ subdirectory which points to a city in the same timezone as you.
For instance, I live in Temecula, CA, which is just north of San Diego, and in the same time zone as Los Angeles. Here’s what I did:

 $ cd /etc/timezones/North_and_Central_America/
$ ln -s Los_Angeles Temecula 

Now when I go to the Time preferences applet, Temecula shows up in the scroll box!