Although when it comes to being one of the best code editors for GNU/Linux nothing beats the GNU-Emacs!. But unless you're a bit familiar with its GUI and certain features are implemented as commands, etc then if you're looking for something that's more simple + less frighting ;-) then Editra is a pretty good one.
As with Emacs, Editra (written in Python) can also be used as a text editor as well but it's mainly aimed at programmers nonetheless.
*. Auto completion support for languages such as XML, Python and HTML.
*. Change font and size.
*. Style editor.
*. Syntax highlighting for more than 60 programming languages.
*. FTP/remove file editing support.
*. Code folding.
*. Auto indent.
*. Save in according to your language container format.
*. Find and replace.
*. Zoom in and Zoom-out.
*. Plug-in support.
*. "Preference" window for additional settings editing.
*. HTML, LaTex and RTF generator (exporter).
*. Line edit.
*. Word wrap and Redo/Undo are just a very little of its main features to mention.
You can install Editra in Ubuntu 11.04 Natty Narwhal, 10.10 and 10.04 by using the below command in your Terminal window.
sudo apt-get install editra
As said we can use it as a text editor but clearly we're not the targeted audience it seems. But if you're a programmer who's looking for a powerful yet a simple looking code editor, then Editra is an excellent little application.