Displays the status of the previous command run from the terminal. Place somewhere inside of your `.bashrc` file. Result: http://i.stack.imgur.com/r7YwR.png

.bashrc

# Shows the exit value of the last executed command
function previous_command_status() 
{
	local exit_code=$?;
	case "$exit_code" in
		0)   printf "\033[1;4;32m%-${COLUMNS}s\033[00m" "Command successful";;
		126) printf "\033[1;4;31m%-${COLUMNS}s\033[00m" "Permission problem or command is not an executable";;
		127) printf "\033[1;4;31m%-${COLUMNS}s\033[00m" "Command not found";;
		130) printf "\033[1;4;31m%-${COLUMNS}s\033[00m" "Script canceled";;
		*)   printf "\033[1;4;31m%-${COLUMNS}s\033[00m" "Command failed with exit code $exit_code";;
	esac
	return $exit_code;
}

PROMPT_COMMAND="previous_command_status"

Still needs some ironing out. For example, it will display after you have run clear on the screen (which is a bit annoying) and it runs once when you first start the terminal instance, even if you haven't run a command yet.