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.
