Cliffhaven Vampire is a bit expensive to cast, but it is a solid 2/4 with a wickedly good ability, so it's definitely worth the casting cost. It's so good that mid- to late-game this card has won me games as I just draw, cast a creature, and do nothing because of all of the synergies with the other cards. With that said, it's also one of the first cards to go when it comes to sideboarding because I normally need to get a card with a lower CMC in when playing against heavy aggro decks. It stays in the deck about 50% of the time, so it is worth keeping it mainboard.
Drana, Liberator of Malakir is amazing, and has largely fallen off of people's radar. She can add amazing firepower to this deck when she shows up. However, because she is a bit of a lightning rod, only 2x to make room for a couple of other cards.
Drana's Emissary is one of the main features of the deck. Passively depleting my opponent's life total and a flier. Very good card.
Expedition Envoy is the quintessential turn 1 card-- a 2/1 for is great.
Kalastria Healer is another banner card for the deck. It has complete synergy with all creatures in the deck, so it allows me to gain life while draining my opponent's life, just for casting creatures (and there are plenty of them in this deck).
Metallic Mimic is one of the new additions to the deck. Declaring this creature as an Ally as it is played facilitates all other cards that work off of the Ally trigger, with the lone exception of trying to bring it back onto the battlefield fromt he graveyard with March from the Tomb. This is pretty much the only flaw. Like Drana, Liberator of Malakir, it is a lightning rod, but its effects can be used the same turn it is cast, so casting Metallic Mimic and following up with another ally gets that other creature a +1/+1 counter, and that's worth it.
Vampire Envoy is just useful. It flies, it's a great defender with 4 toughness, and if you tap it you gain life. Enough said.
Zulaport Cutthroat is just a great card. 1x on the battlefield, is annoying to an opponent. 2x starts getting quite painful for an opponent. 3x is insufferable against any deck. This is generally a cornerstone of Ally decks (with Kalastria Healer), and for good reason.