simple CL text editor : nano
advanced CL text editor : vi or emacs
simple text editor : gedit
basic text editor : abiword
basic online text editor : Google Documents
fancy text editor : OpenOffice Word Processor
fancy online text editor : ThinkFree.com
professional document processor : Lyx
Abiword is great for those that love or need low use of resources, don't like memorizing anything, and just want to start putting their ideas down. I am a fan of gedit, but it only handles plaintext. Google Documents has the same features as Abiword, but everything is stored online.
If you need images, fancy layouts, or tables; you are going to want OpenOffice. Much more resource heavy, but gives you all you could want and a bit more for those familiar with Ms Word 98 - 2003. ThinkFree.com has just about everything the average user would want to do, but missing some of the features of OpenOffice most people don't even know about.
A highly under rated application is Lyx. Ever notice that professionally published documents typically have a certain clean feeling that at first thought seem impossibly complicated to manage in a program like OpenOffice? that is because professional publishers use a language called TeX to do all the work for them. TeX is like a printing / layout programming language. TeX is difficult, but is made much easier with something called LaTeX, which basically adds macros for making common tasks simple rather than having to know every little detail of what you want to do. Lyx takes it to a whole new level with what they call a WYSIWYM word processor (What you see is what you mean). The annoying thing with fancy word processors is not making the layout, but going back and fixing or doing fine adjustments. Trying to get things lined up frequently requires fine motor skills with the mouse, and carefully eyeballing everything you do. Lyx makes it easy to create a layout, and allows you to see the straight forward LaTeX code that lets you know for certain things are the way you want. My favorite part is that layouts (like bibliography, glossary, index, table of contents) are all data driven. For example, with the built-in BibTeX, make a reference in text, and it automatically adds the entry into your bibliography. From the Gui, the data for that reference can be minimized. You can also use a reference in multiple places throughout a document, and LaTeX understands that you are citing the same reference and will only make one entry.
There can be a little bit of time to setup a new document, and the learning curve for everything can seem a bit high, but if you need to make professional looking documents for publication of more than ten pages, it is worth your time in the long run to learn it. Your 10 page documents will be easier to manage and tweak to look just the right way without the usual poke & hope that often fails. For large, fancy publications, Lyx enables you to do amazing things that would be otherwise impossibly difficult in an application like OpenOffice. Ever wonder how Dummies books are put together, or math textbooks? Think it would be impossible in word? Your right! They use LaTeX. Lyx makes LaTeX easy and familiar.