I would personally like to make a new breed of giant, winged velociraptor, which has its own bite initiative in addition to its rider's attack.
Less Giant raptor, and more Steed looking like Raptor, although still with Thick, Strong therapod legs of the superior subset of dinosaurs ... and vicious teeth. In this case, being a steed, probably a broader, sturdier midsection. Also, the sickle claws would come less in-handy here, except for if you made them their own unit, un-ridden, although I would still like to see some raptor-riders out there.
I do agree that investing in flying horses, such as pegasi, should be possible. Also, I have seen far less evidence on these forums than I would like, on the notion of hiring a dragon to join you. Wasn't it stated earlier in the realm of possibilities somewhere? Im thinking defeating it in battle + a large sum of gold should be a good cost for hiring a dragon.
Or alternatively, you kill the dragon, and grant its eggs/hatchlings to a Master Beast Trainer/ Beastmaster, and raise the younglings Or singular youngling, to join your army. If this was the case, it might be as significant a time investment on that one little dragon as your entire empire. might even have a body guard built around it called a "dragon-core" ... and when it gets old enough, and out of its own decision decides to stay with you, you could make a soul-pact with the dragon to make it the next heir. (or alternatively, granting your Sovereign immortality as long as the dragon lives)