My lightweight solution is to append `&& tput bel` to long-running commands, to ring the terminal bell upon completion :) Requires sound of course, but it's reasonably easy to remember and quick to type. eg. try `sleep 5 && tput bel`

I've also used a similar cheap hack to listen to web traffic... Just write a bell character to your server log when something interesting happens, then `tail -f` the log file for live data sonification!