It seems that EditPlus has a code completion file for Stata. I have never used this program but this seems to be what you are looking for.
Edit: Did a quick search and found this post, http://enoriver.net/index.php/2008/09/10/edit-stata-do-files-with-notepad-2/ It seems that you can setup Notepad++ (FREE!) to run with Stata quite well, might be worth looking into.
