Have you looked at arc-welder (arc IDE distributed with rainbow, uses java/swing for UI) ?
You can evaluate code from the IDE, although for the moment output goes to the console. This is trivial to change though. I've just recently added a crude jump-to-definition feature so it's quick and easy to find function and macro definitions. Screenshot at http://www.fnargs.com/2009/05/introducing-welder.html
I'm preparing a new, faster rainbow which will hopefully be ready in the next few days. Let me know if you're interested in trying it out.