Emacs is a wonderful text editor. It has huge power once you become a power user. You can access a shell, have as many files open as you want in as many sub-windows and an extremely powerful scripting support that lets you add all kinds of neat features.
I have been using a ruby-mode which adds syntax highlighting and whatnot to ruby, and the same exists for every major language.
If you keep at it, you can use exclusively the keyboard and never touch the mouse, which increases your editing speed by a significant margin.
If you want to start with something a lot more basic though, gedit is nice... it has built in syntax highlighting as well for most languages based on the filename extension. It comes with the OS as well (though emacs you can easily install with apt-get or some similar package finder utility).
UPDATE: I think gedit is exclusively GUI based though, so it would be useful to learn emacs in case you are stuck with just a shell (it is fully featured in both shell and graphical mode).
FURTHER UPDATE: Just FYI, I am not trying to push Emacs over Vim, it's just what I use, and it's a great editor (as I'm sure Vim is too). It is daunting at first (as I'm sure Vim is too), but the question was about text editors on Linux besides vi... Emacs seems the logical choice to me, but gedit is a great simple text editor with some nice features if that's all you are looking for.