Its a shame though because it makes a lot of sense with counter decks.
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Oh and taking a look at the zombie deck I just made may give you ideas: http://www.mtgvault.com/ViewDeck.aspx?DeckID=290955
Devil's Play may be better for you than Red Sun's Zenith (because of flashback). And it's 'Standard'. :)
Maybe Vengeful Pharaoh?
Maybe a Grave Titan?
it *won me a lot games xD
If I may suggest tweaks in your layout: CREATURES 2xVampire Nocturnus 3xBloodghast 3xGatekeeper of Malakir 1xMalakir Bloodwitch 3xVampire Hexmage 3xVampire Nighthawk 1xAnowon, the Ruin Sage 2xBloodline Keeper 3xKalastria Highborn ENCHANTMENTS 2xSanguine Bond LAND 2xDark Depths 1xVolrath's Stronghold 1xUrborg, Tomb of Yawgmoth 16xSwamp PLANESWALKERS 1xSorin Markov SPELLS 2xDemonic Tutor 2xDark Ritual 4xGo for the Throat 2xBlood Tribute 2xExsanguinate 4xDismember SIDEBOARD 3xSurgical Extraction 3xDoom Blade 3xRatchet Bomb 3xLux Cannon 3xWitchbane orb These are all suggestions,so take what works for you. I'll explain them. I took your Sanguine Bond/Blood Tribute Combo out of your sideboard because it works well no matter who you're playing against. I used to run it and it one me a lot of games. I took a Sorin Markov out to make space, since he's one of your most expensive to cast. I took out Vampiric Tutor because Demonic Tutor doesn't cost you life and puts it right into your hand. I took out Lake of the Dead and Petrified Field to simplify your land base. Besides, Dark Ritual is already a source of mana ramp. Nice call by the way on the Vampire Hexmage/Dark Depths Combo. :) Instead of Damnation, I suggested Dismember. Really good specific creature removal that won't harm your creatures. Also Exsanguinate I believe is a better Choice over Sorin's Vengeance, since its only as expensive to cast as you want it to be. Also, I suggested a sideboard more geared toward what ifs, like playing against curse decks, or artifact decks... I hope you can make some use of this. :)
More bloodthirst, maybe.
You may want Hull Breach and Elvish Lyrist to get rid of control by means of enchantment. Maybe too much focus on anti-counterspells as that's for the most part only blue and not as common as other types of control. Troll Ascetic/Gladecover Scout and Ranger's Guile are good for hexproof which will prevent creature control.
Crucible of Fire would compliment your dragons nicely and Dragonspeaker Shaman may improve the speed of your deck, especially as both of their effects stack. It may also not be a bad idea to fit broodmate dragon in there, as if you bring it in with Zirilian, the 4/4 dragon token will stay in play. Sarkhan the Mad would be good too, since it would allow you to sacrifice your dragons for permanent 5/5 Dragons and make it easier for you to bring them back out with Bladewing.
You should probably pick between Kaalia of the Vast and Karador, Ghost Cheiftan as they have similar effects. I would go with Karador, since his effect is slightly better. With all these huge creatures, you'll need more mana ramp.
You may want to consider fitting Wilt-Leaf Cavaliers in, as you can use either one of your colours to cast it and its good for the cost. Not to mention its an ideal blocker with vigilance. Wilt-Leaf Liege is also a good idea to go with your dual colour creatures. Benalish Veteran may be a better choice than Knight of the White Orchid as you already have another first strike creature that's more valuable. Hero of Bladehold may very well be something you don't need. Shield of the Oversoul may also be a good idea. Good call on the Coat of Arms. Beacon of Immortality is a bit expensive and perhaps overkill. Why not Dawnglow Infusion or Heroes' Reunion? Also, you may want to make room for control/removal. Oblivion Rings, Gleeful Sabotage, or Aura Shards may be good ideas.