If you don't want a full on IDE, there's Text Wrangler, which is pretty popular with programmers.
Personally I use TextMate, when I'm not using MacVim (also installable via MacPorts). If you're from the Emacs school, there's Aquamacs. Or course, Terminal versions of both vim and emacs are preinstalled.
It doesn't download and compile packages and tools already present on the system. This makes it smaller and faster, but less robust, since an update from apple could potentially break dependencies. Macports is self contained in the /opt folder.