TabMate (modeline support)
Håkan Waara has written a plug-in for TextMate which add modeline support.
What is a modeline?
Ever since the first day of UNIX, text editors such as vi and emacs would insert a line at the top of text files with options specific to that file. Options include things as what language the code was written in, the size of tabs, whether to use spaces instead of tabs, et cetera.