Try this famous tongue twister. Say it as many times as you can (at least three times).
Peter Piper picked a peck of pickled peppers. If Peter Piper picked a peck of pickled peppers, how many pickled peppers did Peter Piper pick?
You can listen to it here, and if you have an account with Voice Thread you can leave your own recording or comments (don't worry it's free).
More Tongue Twisters