Emacs can do all of this, though real thorough code completion is really dependent on the support of and mode for the language you're using. There are a whole bunch of generic completion minor modes too, so you'll never be completely without it if you don't want to.

For perl, I don't really use the debugger much at all. You may also be interested in Sepia, which runs an "inferor perl" more or less like Slime for Lisp, which means it can catch/debug exceptions when they occor, do completions based on whatever is currently defined in your running perl process etc. This is a pretty different way of developing than the usual save/compile/run methods, and suits some kinds of programs better than others.