NotepadPlusPlus has several mentions on the NotePad page and is currently (2012) being developed.
(http://notepad-plus.sourceforge.net/uk/site.htm)
NotepadPlusPlus and NotepadTwo? are similar, but they're GNU freeware. I use them all the time: when coding in MatLab or VhdlLanguage for my electronics subjects, or when I have to program with Java. They support syntax highlighting and the works. See http://notepad-plus.sourceforge.net and http://www.flos-freeware.ch/notepad2.html to get them. (Addendum: As of 2012, Notepad++ has literally grown into an IDE, and a pretty nice and lightweight one at that. It has a DBGP debug plugin, which lets you step through your code and check your program's state within Notepad++. Combine this with the PHP Xdebug extension and you got yourself a kinda ramshackle PHP debugger -- but also lightweight and better than nothing. --DaNuke?
It supports markup for an impressive list of different languages.
I've found it very buggy and poorly designed. Open a readonly file with autosave turned on, leave your desk, and you will return to a screen full of "Could not save file" errors.
Hmm. I didn't use it long enough to discover the bugs. I only used it long enough to find that it lacked any of the useful features of a modern editor and promptly aimed it at the ashcan. Programmer's Notepad is a far better editor, and there are all kinds of Eclipse variants out there mucking up the editing world with their own interpretation of the CUA. Whatever.
Editors will come and go as long as there are people who think they can do a better job of it. Let 'em have at it.