For my money:
Mounted Combat
Ride-by Attack
Spirited Charge
Trample
Cavalry Charger (from Complete Warrior)
Combat Reflexes
I think Cavalry Charger will end up being surprisingly powerful. Against a single target, your level 16 character should have no trouble passing the DC 20 Ride check for 4 extra points of damage with Leaping Charge... with a lance, that's a nice big +12 damage. If the PCs are nice enough to line up, Fell Trample (you may attempt to overrun multiple targets while mounted) will own the bejeezus out of them, since the mount makes the Strength check to knock them over. It gets an attack (at +4) against each opponent you knock over, and you'll both get attacks of opportunity as they rise (depending on your choice of weapons).
Also, don't forget to get 5 ranks of Handle Animal for the synergy bonus to Ride checks, and don't forget to use Mounted Combat every round!
Mounted Combat
Ride-by Attack
Spirited Charge
Trample
Cavalry Charger (from Complete Warrior)
Combat Reflexes
I think Cavalry Charger will end up being surprisingly powerful. Against a single target, your level 16 character should have no trouble passing the DC 20 Ride check for 4 extra points of damage with Leaping Charge... with a lance, that's a nice big +12 damage. If the PCs are nice enough to line up, Fell Trample (you may attempt to overrun multiple targets while mounted) will own the bejeezus out of them, since the mount makes the Strength check to knock them over. It gets an attack (at +4) against each opponent you knock over, and you'll both get attacks of opportunity as they rise (depending on your choice of weapons).
Also, don't forget to get 5 ranks of Handle Animal for the synergy bonus to Ride checks, and don't forget to use Mounted Combat every round!