Bleed

I wouls suggest Bloodghast as he will be constantly coming onto the field and allowing you to cast Feast of Blood when your opponent may not expect it. If you do decide to add Bloodghast then I also suggest adding in the fetch lands so that you can have them come back when you need them not just when you draw a land.

Blade of the Bloodchief can be incredibly useful in a vampire deck.

I would replace Hideous End with Doomblade because the two damage is not often worth the one extra mana, especially if you need a turn 2 doomblade.

Also, Sign in Blood is an amazing card, especially for a vampire deck where you usially have a fair amnount of lifegain. Drawing 2 cards for 2 mana is absolutely amazing.

I would ditch grim discovery, for one reason you NEVER (yes there are land kill decks, no you would not mainboard for them, or hell even sideboard for them because they are rare) will have lands going into the graveyard, if you insist on adding in some graveyard return cards add disentomb or Soul Stair Expedition.

I wouldnt run Bloodseeker, mainly because if you arent playing a creature heavy deck he does nothing for you, perhaps place in Guul Draz Assassin or another of the 1B vamps that gets a benefit from opponent being 10 or less life,

Now, speaking for the cards that get benefit when an opponent has 10 or less life. Sorin Markov or Blood Tribute, both would go leaps and bounds towards accomplishing that goal, although they do have the hefty 5CMC mana cost (I believe) but allow for some fantastic things.