If you do a lot of xml and or xhtml editing, consider EMACS as your first choice xml editor.
EMACS is a very powerful text editor created by Richard Stallman several years ago. It was greatly appreciated by developers for its power and flexibility. In the last ten years, the advent of advanced IDEs (complex environments for developing programs) has obfuscated the fame of EMACS, and currently the number fo developers working on EMACS is not that huge.
