[frio]

There's TextMate on Mac, and e-texteditor for Windows (which is a port of TextMate)... but that leaves Linux high and dry until the developers finish porting it there too. It requires cygwin under Windows too :/.

Other than that, there's SciTE, which is quite nice. Notepad++ on Windows is a derivative thereof.

[chbarts]

Nedit http://www.nedit.org/ might be too much like ass for you, but it's pretty simple in the default state and isn't just a GUI wrapper around a character-terminal editor.