Check the rules surrounding 'magebred' animals out of the Eberron Campaign Setting. Good rules for amping existing animals in a decent amount of ways (ie, stats, speed, ac, etc).
If you are going to stay pure fighter, there isn't a lot. The link Thanee supplied is the best.
After that, in Eberron you could consider a magebread warhorse. Lastly, you might be able to get the DM to let you buy an "advanced" horse.
After that, the awaken/leadership option is as good as it gets. I've got a VoP sorc. who has an awakened mule (cleric) via leadership. Darn handy that.
Since it's in Eberron, try to get on the good graces of House Cannith and get a discount on an Effigy Heavy Warhorse (from Complete Arcane) or a Brass Steed (horse-golem from Heroes of Battle).