regardless of where you're at on Disney World property, ALL of the fountain drinks are Coca-Cola products only. (Also true for soda in the table service restaurants. Some restaurants also have specialty bottled soda, like Via Napoli/Italy/Epcot sells bottled Italian sodas along with Coke products.)
In general, expect Coke, Diet Coke, MinuteMaid lemonade, even the lite version (sometimes the flavored kind, like POFQ has Minute Maid pomengranate lemonade) Also Sprite, Sprite zero at some places, Caffeine free diet coke, rootbeer, Powerade. Not all fountains have all flavors/varieties but expect a selection of diet/non-diet/caffeinated and non-caffeinated beverages from Coca-cola.
And yes, Iced tea is available too.