The text related tools chapter is the largest in this guide, most of the time on a GNU/Linux machine you will spend time interacting with text. This chapter briefly covers text editors and goes into more depth on viewing text, using tools to manipulate text, finding text within files and changing text formats between windows based systems and GNU/Linux based systems.
A traditional UNIX system text editor, should be on any UNIX system. It requires learning a few key combinations, but is very powerful, and it is also quite small. vi is well known for its minimal use of resources.
vim: vim - vi improved. A newer version of the vulnerable vi editor. Many systems use vim rather than vi.
More than just a text editor. This text editor has a steep learning curve but is also very powerful, it is both advanced and quite large. emacs can do anything, surf the internet, chat, play games and many other tasks.
There are too many different text editors to list here. Have a look on the internet, either search for them using any search engine or you will find many of them at Sourceforge or Freshmeat.