Lore lesson time
Tauren and Trolls aren't the type to work together. Tauren call upon the powers of nature, such as shamanism and drudism, while trolls call upon magic and power channaled from the spirits they worship, known as the Loa. If it weren't for the orcs saving both of their asses, they wouldn't so much as look at each other
Dwarves you could do something with I guess. Would be interesting if you didn't go the normal Ironforge dwarf route and instead chose their shamanistic breathren, the Wildhammers, or their magic-inclined breathren, the Dark Irons. Wildhammers are the ones with Gryphon Riders, while Dark Irons are the type to summon Fire Elementals
Hmmm, would be GREAT to see someone make a map of Dark Iron Dwarves and the forces of Ragnaros versus the Dark Horde, the classic WC2 variety of orcs, Forest trolls, ogres and goblins, allied with the Black Dragonflight. Might need a bit of WoW knowledge though, but would still be great
Gnomes are techno-crazy allies of the dwarves who ran to Ironforge after irridating their city to try and kill off the invading Troggs. Though, as Wulf mentioned, there aren't too many of them left
