Hmm.. the mana base looks kinda solid, that's already good. just 3 small suggestions.
Evolving Wilds or
Terramorphic Expanse could be replaced with
Ash Barrens, which is a little more flexible.
Obelisk of Grixis could be replaced with Darksteel Ignot. The effect is the same, but the ignot is indestructible. Since you're playing a decent amout of swamps, Tainted
Mountain and
Tainted Isle could be worth concidering.
About the tutors: What about
Diabolic Intent? Sacrificing a creature shouldn't be a big deal with a zombie deck.
For removal, Curtain's Call works gread in EDH, and
Tragic Slip could also be interesting, since it ignores indestructible, and its happends kinda often that creatures die.
A little word about
Chaos Warp: I know that many like it because its a universal removal in red. But I've already seen a
Chaos Warp making things much worse. For example someone removed a threat, and given the player a high cmc combo piece for free which ended the game in the next turn.
I don't want to say its a bad card, but if you want to use it, you should be aware about the down side.
You've added
Urborg and the deck seems like you want to attack alot. What about
Filth then? With
Filth in Graveyard and Urbog out, your whole board becomes unblockable.
If you need graveyard hate in yor meta and/or your playgroup likes to tutor,
Ashiok, Dream Render is a very great solution for both problems.
@CastleBodrin: check the color pie. 82% black, 7% red, 11% blue. so
Izzet signet wouldn't do much.
/edit: some more tribal cards:
Metallic Mimic,
Adaptive Automaton,
Coat of Arms (could be
dangerous against other tribe decks),
Vanquisher's Banner.
/edit2: another
very important card for zombie decks:
Rooftop Storm