I'd move a REPL from the "nice to have" to the "mandatory" list. The interactive shell is really nice when the student just has to learn what a new function or method does.
The most common confusions students have told me about with IDLE are:
1) Mixing up the interactive shell and file editor windows.
+1 for syntax highlighting. Don't discount how colorful text improves the coolness of coding for students. Even if they change the colors to look like a garish MySpace page.