Adaptive Automaton: An anthem on a body. Not a soldier (at least not until it hits the board) but still a workhorse in the deck.
Archangel of Thune: The flying and lifegain is nice, but the real reason she's there is the +1/+1 counters. There is a LOT of lifegain in this deck (Soul Sisters, Elspeth Tirel, Ajani, High Market, etc.), so it's not uncommon for her ability to trigger multiple times a turn.
Auriok Champion: One of four soul sisters in the deck. The sisters are great at offsetting all the damage from self-damage lands. Crazy synergy with Archangel of Thune. The deck runs perfectly fine with the other three sisters if you're put off by the price of Auriok Champion.
Brimaz, King of Oreskos: Barfs out adorable cat soldiers when he attacks or blocks. It's usually pretty easy to find someone you can attack advantageously with Brimaz, just to get the free token. One of the few aggro cards in the deck. Useful for building an early army or recovering after a board wipe.
Captain of the Watch
: Expensive, but an army in a can and an anthem all in one. I'm never disappointed to cast her.
Daru Warchief
: I don't play enough soldiers for the cost reduction to be worth it on its own (only seven, not counting Daru Warchief) but the added pump helps.
Elesh Norn, Grand Cenobite: Flavour-wise, Im not sure the Mother of Machines would want to help an army of soldiers (especially after she "converted" so many cat soldiers on Mirrodin). Still, the +2/+2 boost and pseudo boardwipe is huge. She often puts the army over the top for a ridiculous attack.
Evangel of Heliod: A later addition to the deck, Evangel has proven to be surprisingly useful. Even without creatures, I usually have several enchantments in play, so Evangel often comes with at least 5+ friends.
Field Marshal
: Cheap pump and the first strike is pretty nice. Plus, he's one of Dariens tacticians!
Hero of Bladehold
: Along with Brimaz, she can be an early threat or a great way to recover from a board wipe. Plus, battle cry is useful pump. Unfortunately not a soldier herself. Side note: I really need to get the non-promo version of the card - the art is much better.
Jazal Goldmane: Ajani's dead bro is pretty, pretty good. For four mana your dudes get really big, really quickly. If you have him early game you might be able to knock one player out before they can establish a board presence. Late game, using his ability twice on the same turn is usually GG.
Knight of the White Orchid: Sadly, he's not a soldier (his name is a bit of a giveaway). Still, ramp in white is hard to come by (and he can grab Mistveil Plains). Plus, the first strike is often relevant when there's a few anthems on the board.
Mentor of the Meek
: Card draw is hard to come by in mono white. Sure he's not as good as the UB options out there, but this deck pumps out a ton of soldiers so you're almost guaranteed to draw cards off him. Too many anthems can shut him off, unfortunately. Added bonus: hes a soldier!
Mikaeus, the Lunarch: Another target for Ranger of Eos. A bit slow, but the +1/+1 counters are always welcome.
Mirror Entity
: Another win con. Much like Jazal, Mirror Entity can be activated early game if you think you can eliminate an opponent with an alpha strike. Can be recurred with Sun Titan and Reveillark (uh, if I played Reveillark).
Ranger of Eos: Tutor on a (soldier) stick. Creature tutors are not readily available in white, so hes a valuable addition. One drops in the deck include Soul Warden, Soul Attendant, Weathered Wayfarer and Mikaeus, the Lunarch.
Soul of Theros
: A recent addition to the deck, I'm still not totally souled" on him yet (hah ugh). The ability to give the entire team lifelink is impressive (especially from the grave), but six mana to activate is costly. Yet another non-soldier, but at least the flavour is right.
Soul Warden
: Soul sister #2.
Soul's Attendant: Soul sister #3.
Sun Titan
: One of the best cards in the deck because of its amazing versatility. An obvious move is just to grab a creature from the yard, but it has much better implications for ramp. Being able to bring back Myriad Landscape, Exploration Map (an impending addition), or even excess Land Tax lands is huge for a white deck.
Suture Priest
: (Evil) soul sister #4.
Weathered Wayfarer: He is so good on turn one. In a multiplayer game, he'll be active more often than not (white doesn't out ramp many decks). Can be used to grab a ping land for Darien for later, or High Market for sac shenanigans or Myriad Landscape for ramp, or Ancient tomb for ramp and self-harm etc.