I really like the banner of the steadfast ox. It would be especially great for an Ostland army!
As for the Banner of the Line, it seems a bit powerful. Perhaps it lets the unit that has it (and any detachment in range) ignore the -1 to hit penalty for shooting and lets them stand and shoot regardless of how close the enemy is? It keeps the feel down without letting the unit get off an insane amount of shots.
Also, I've got a few ideas for banners that I'd like to see:
Banner of Sigmar-30 pts?
This banner bears the symbol of the twin tailed comet and it has been blessed by a priest of Sigmar. Warriors fighting beneath it take courage from it to fight against the dark and unholy.
The unit is immune to fear.
Banner of Discipline-25 points?
Comissioned for Count Steinhardt, this banner is woven with potent magic which remind the warriors near it of their training. Thought lost after the disaster of Mordheim, it was recently recovered and is now kept in Altdorf.
The unit that bears this banner may re-roll failed panic and rally tests. Any detachment attached to it gains +d3'' to their charge range when making a supporting charge or gains +1 to hit when standing and shooting at an enemy which charges its parent unit.
Banner of the Glorious Charge- 20 points?
This banner instills courage in those who ride under it. When they see the enemy coming, they will spur their steeds onward and meet it head on.
Knight units only. If charged in the front, they will counter-charge the enemy. The enemy unit that charged will still strike first, but the knights get +2 str from their lances (if armed with lances) for the first turn of combat.
Banner of the Matyr-10 points
Woven by the paranoid General Otto von Oswold, this banner instills great devotion for their leaders into the men who hold it. Many men have died under this banner, but their deaths have usually ensured that their leaders have lived to see another day.
Heroes in the unit automatically pass look out sir rolls. Furthermore, unit champions that declare challenges may nominate an enemy character who must accept or decline it.