Use the reset command.
See man reset:
When invoked as reset, tset sets cooked and echo modes, turns off cbreak and raw modes, turns on newline translation and resets any unset special characters to their default values before doing the terminal initialization described above. This is useful after a program dies leaving a terminal in an abnormal state.
It's useful for lots of situations where the terminal is acting up, like if a script has turned off local echo and died before turning it back on so you can't see what you're typing at the prompt...