vi A traditional UNIX system text editor, should be on any UNIX system. It is fairly difficult to learn but quite powerful, it is also quite small and uses minimal
amounts of resources.
vim - vi improved. A newer version of the vulnerable vi editor. Many systems use vim rather than vi.
emacs 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 you will find many of them at Sourceforge or Freshmeat.