My favorite is X11's select-to-copy, middle-click-to-paste feature. It bewilders me that this isn't standard on all platforms. It only takes two simple clicks to copy and paste, yet some people find it unintuitive (or even downright hate it). I think it's a huge time-saver.
This was instantly what came to mind for me, followed by tab completion in the shell (expanded by the bash-completion package to become utter perfection).
Utter perfection is unfortunately limited to ZShell's bash completion, but I know what you mean - I experience it every time I log into a Solaris box and have to use CSH.
Don't get me wrong, Cshell is good too syntactically speaking, but the completion on Solaris 8 is a little, meh.
BTW - we have a dojo with different versions of Solaris going back to god knows when, that's why I'm using CSH - would not use Solaris 8 in production anymore.
