SciTE is a light-weight, cross-platform, fast text editor I always use. For example, on windows platform, it can be a single exe file you can copy to anywhere you like, and smaller than 500k, which is much smaller than editplus and ultraedit.
Despite of its small size, it is highly configurable, there are menu items to edit its default properties, e.g., whether to show line number, where to wrap long line, etc.
For example, the following four lines make scite wrap and show line num automatically, and prompt a user to reload a file when the file is changed out of scite.
For more documents, please refer to http://www.scintilla.org/SciTEDoc.html