It's geek day here at marginalia - I've recently switched shells to zsh. Any command line user knows that switching shells is usually more trouble than it's worth, but I'm glad for the switch for one simple reason: intelligent completion. I've often wished that when I type a command and check for completions it only give me the appropriate files. For example, if I'm using tar, when I type tar and then TAB on the command line, most shells will prompt you with all the files in the directory. zsh will only complete with tar files. It is, of course eminently configurable, because this is unix.

My only remaining wishlist item is for a xterm/shell combination that would let me use a scrollwheel to navigate history.