Klaus said:
Here's a thought, Ari: throw at WotC the idea of a mounted-combat "Complete" book, like Complete Knight or Complete Rider.
Bundle it in with familiars and animal companions.
Rules for swarm companions, combining Leadership with Improved Familiar, Living Spell familiars, feats to add lesser companions like a Beastmaster, spells and feats from the website like Wild Cohort, undead familiar, planar familiar, elemental familiar, etc.
Stunts and Tactical Feats for mounted combat. More detailed rules for grappling etc vs a mounted opponent. Proper errata for Ride-By Attack. Rules for cavalry formations.
Paladin's Mount variations for those who don't like the Pokemount model. More detail on the Summoning variant for always summoning the same creature. Some long-duration Summoning spells for non-combatant creatures.
Lots of wondrous items for familiars, companions, and mounts.
Prestige Classes and substitution levels for awakened animals, with hints for how to make them work as PC races. Awakened horses with paladin cohorts, and awakened cats with gnome familiars...
You know, that could be pretty damned cool...
-Hyp.