What is a decent IDE for developing JavaScript, I'll be writing both client side stuff and writing for Rhino. Ideally It needs to run on Mac OSX, although something that runs on Windows too would be nice.
ADDITIONAL:
Having had a play with both js2 and Aptana, I think I'll be continuing to use Aptana. Mainly because I find emacs a bit hard to get my head round, although I did think that the error hi-lighting in js2 was better than that in Aptana.
I'm still looking for a way to visually debug my js code that is running atop Rhino...
Aptana IDE, absolutely. Stable, great syntax support for all the major javascript libraries, very good css and html editors. Also good support for php, air, ruby on rails and iPhone app development (I never tested this one). Aptana can also connect to remote site via ftp (sftp in the pro edition) and to svn and cvs repositories. It's based on Eclipse, so it's not exactly a lightweight application. But it's really, really good. You can also use it as an Eclipse plugin if you develop java wab app, but when I tested it in this version, about 1 year ago, it was not stable. Much better to use the standalone version.