the one my family goes by is...

January - Garnet
February - Amethyst
March - Aquamarine
April - Diamond
May - Emerald
June - Pearl (some say Alexandrite)
July - Ruby
August - Peridot
September - Sapphire
October - Opal (some say Tourmaline)
November - Topaz (some say Citrine)
December - Turquoise (some say Tanzanite)