I've been known to act in a play or two from time to time; and during performances, we used this trick to keep slamming doors from disrupting the performances.  But it's just as effective at keeping doors at home from waking up your little ones!

Now you don't have to spend way too much time closing the door extra slowly, only to have it shut just loudly enough to wake the baby anyway!

Just put some felt in the door frame...