I'll share what I've been using. It's called Notepad++ and can be found here: http://sourceforge.net/projects/notepad-plus OR http://notepad-plus.sourceforge.net/uk/site.htm
I've had no problems with it viewing all the files in the data directory, and when it comes to actually wanting to mod an xml file its pretty nifty there. It's GNU General Public License, so free to download.