Grassfrog

If you depend on the ability of "The Butcher of Malakir" him being a creature is a great weakspot, since it is easier to remove a creature than an enchantment/artifact from the battlefield. Try "Dictate of Erebos" or "Grave Pact" instead.

"Pawn of Ulamog" may be a great addition. You can sacrafice twice as much, and do twice as much damage. That makes your combo faster and more deadly. And while we are talking about twice as much... Maybe add a "Blood Artist". It may only deal damage on target player, but therefore you again can deal faster, more damage.

"Grim Haruspex", or "Dark Prophecy" may also be a useful addition/alternative, but not really needed if you dont want it since you have "Altars Reap".
"Bloodghast" makes great use of the sacrafice circumstances, but is a bit pricey in terms of money :/

I myself play a sacrafice deck, and have played vs one. Both links below.

My deck:
http://www.mtgvault.com/grassfrog/decks/vampirism-is-about-sacrafice/
My friends deck:
http://www.mtgvault.com/mungo08/decks/modern-gb-sacrifice/

if you want more draw you can consider "Faithless Looting". It also has the oppurtunity to discard.
I pretty much build the same deck, just a little more creatures ( i tried to be aggressive there).

http://www.mtgvault.com/grassfrog/decks/bloodrush/