I think this is really neat!

http://www.sevenwires.com/play/UpsideDownLetters.html˙˙˙oʇ oƃ noʎ ɟı uʍop ǝpısdn ǝdʎʇ uɐɔ noʎ ˙ןןǝʍ ɥo ˙ɥɐǝʎ˙˙˙˙os 'ʇuǝɯoɯ ǝɥʇ ʇɐ ʇnoqɐ ʞןɐʇ oʇ ǝɯosǝʍɐ ʎןƃuızɐɯɐ ƃuıɥʇʎuɐ ǝʌɐɥ ʎןןɐǝɹ ʇ,uop ı ʇnq 'uʍop-ǝpısdn ןןɐ ʇı pɐǝɹ noʎ ǝʌɐɥ uǝɥʇ puɐ ʎɹoʇs ƃuoן ןooɔ ǝɯos noʎ ןןǝʇ pןnoɔ ı ʇɐɥʇ ɥsıʍ ʎןןɐǝɹ ı ¡ʎɐʎ ˙uʍop ǝpısdn ǝdʎʇ oʇ ʍoɥ pǝuɹɐǝן ʇsnɾ ı 'ʎןsnoıʌqo os 'ʎɐʞo