The Worg-Goblin (or Wolf-Goblin) mesh up is classic cool, and has a lot of ramifications for the flavor of your goblin tribes that doesn't rely on them being bullied by the bigger, tougher goblinoids. Of course, those bigger, tougher goblinoids (hobgoblins, bugbears) have their own wolf companions, as well...
Kobolds IMC focus on flightless birds as their mounts and companions, and enjoy parrots and the like as talkative allies (Kobold Pirates!). They are also avid users of dinosaurs of all types.
Orcs go with swine -- boars, pigs, etc. Nothing rapages quite like an orc chieftain on a dire boar coming into an unsuspecting town.
Dwarves IMC don't have much in the way of mounts. Being subterranean, mounts don't make a whole lot of sense. Their technology (elevators, shafts, mine carts) are their horses! Still, they make use of some domesticated animals -- bats, for one, are very useful to them.
Gnomes have affinity with creatures like badgers, foxes, and weasels. Things that are small and fuzzy and live in burrows make good companions for them, and for mounts they employ larger versions (gnome druids astride dire badgers!)
Halflings are basically feline kind of things. They like small cats, and even larger cats have their place in the mythos. Their gods are worshiped as jaguars.
Ogres prefer big and strong animals -- rhinos, hippos, and elephants, which they cow into submission.
Lizardfolk groove on other lizard creatures largely, including crocodiles, and they travel through land on the backs of large tortoises. It's something of a theme for them, and such creatures can make swampy portages easy with a lot of equipment.
More piscine humanoids like Locathah and Sahagin make use of sharks, barraccuda, and piranha depending upon where they're living at the moment.
Elves like birdies, themselves. Giant eagles, giant owls, giant hawks, anything that can fly and make elves feel like they're really looking down on everythinge else...
