Ok, some other things I'd like to add.
Motivate Care: I know the boards like to say "AC is worthless, just get miss chance." But for a lot of groups and IME, AC is useful. You rate motivate attack highly, but for a party with typicla role variance, there will only be a few melee attackers, possibly a ranged, and some casters who may or may not melee at all. Motivate Care buffs everyone in the group constantly. And as an untyped AC bonus it should add to touch AC, which is always nice. It's my favorite major aura.
Feats: I like Daunting Presence a lot. It's an at will ranged fear effect with min/level duration that you can fear stack with intimidation. Combat Panache isn't hard to qualify for and lets you debuff a foe's attacks against you by your charisma modifier. Nymph's Kiss gives +2 to all cha-based checks (or just skill checks, I forget) along with bonus skill points and a small save bonus. Force of Personality also bears mentioning, though it only boosts will saves against mind-affecting.
Classes: Warblade is synergistic for the same reasons Crusader is (White Raven stuff) and also brings IH Surge to the table, to shrug off effects that would keep your troops from benefiting from your command voice, plus has Diamond Mind save counters, too. Both classes work really well for a charge-based Marshal.
Prestige Classes: Outcast Champion (Races of Destiny) gives a will save bonus aura, makes aid another grant a +4, and at 5th level gives you the ability to impart a rage-like effect on a whole group. It's only a 5 level class. Menacing Brute from the same book fits with the Dread Pirate / Scarlet Corsair type builds for intimidating, nothing to really boost the group, though. At the 5th and final level, you get an area effect cower everytime you drop a foe, though the DC is a little low (fixed at 15 + cha; +4 if the felling blow was a crit).
