There is a very active question about LaTeX editors and IDEs. I personally use Vim with LaTeX-suite for any LaTeX editing, and I am very happy with it. Lately I began to use ConTeXt more and more. I would like to know what people use for editing ConTeXt. Especially is there is a set of Vim macros similar to LaTeX-suite.
I know there is a page about Vim on ConTeXt garden, but as far as I can tell, it has not been updated in quite a while.
Hans Hagen (the author of ConteXt) uses SciTE and, more recently, textadept. He also wrote support files for those editors and these are part of the ConTeXt distribution. The ConTeXt distribution also comes with a full set of support files for TeXWorks. The support for the various other editors mentioned above and on the ConTeXt wiki page are written by other people.
If you want the best possible editor support, you should probably use one of the three that are actively supported by ConTeXt, but I have heard that Emacs and TextMate (at least) are also working well.
As a devoted Emacs user I prefer using AUCTeX, which supports ConTeXt. Another useful Emacs addition is etexshow, which is an Emacs port of texshow, a browser for ConTeXt commands (not all, but most of them).
I use Kile. I found a syntax highlighter at KDE-files.org. I modified it based on the LaTeX highlighting file to (1) allow spell-checking only in text sections and (2) show section* headings in bold. I prefer to use the extensions, .mkii and .mkiv to prevent confusing the text editor. You may want to change that. You can find it on PasteBin. Save it as ~/.kde4/share/apps/katepart/syntax/context.xml.
For a few days now I am using textadept.
It's similar to SciTE (imo faster), as customizable and lightweight and surely worth a try.
I posted a question and answer here on stackexchange how to set it up for ConTeXt: