UR Eldrazi 6/10

4x Drowner of Hope
3x Ulamog, the Ceaseless Hunger (shave 1 v. aggro)

4x Clash of Wills
4x Spell Shrivel (shave v. humans and other aggro MUs)
4x Hedron Archive
2x Anticipate
4x Spatial Contortion (cut v. non-manland control)
3x Kozilek's Return (shave down to 1 often, leave one to have Ulamog clean up on flashback)

2x Chandra, Flamecaller
2x Jace, Unraveler of Secrets (often shaving 1-2 in aggressive match ups)

4x Highland Lake
4x Shivan Reef
4x Wandering Fumarole
4x Shrine of Forsaken Gods
4x Mage-Ring Network
2x Spawning Bed
6x Island (shave 1 if you REALLY need to)

SB:
(Anti-Aggro)
2x Rending Volley
1x Kozilek's Return
2x Fiery Impulse
2x Roast

(Anti-Planeswalker)
3x Negate

(Anti-Control)
1x deceiver of forms
3x Reality Smasher***
1x Kozilek

Green White Tokens
-2 Clash of Wills, -1 Spell Shrivel, -1 Mage-Ring Network, -1 Jace, Unravel of Secrets
+3 Negate, +1 Kozilek’s Return, +1 Deceiver of Forms

Because this is the most popular deck I will give some tips in addition to the sideboard guide.
There are two easy was to lose this match-up:
First, not being able to counter turn 4 Gideon.
Second, flashing back Kozilek’s Return into flashed in Archangel of Avacyn.
Do not Spatial Contortion Sylvan Advocate if they have Dromoka’s Command mana up.
Often the best value you’ll get out of Kozilek’s Return initial cast is killing one or two Plants/Ally tokens--do not wait and hope for better, it is important for it to be in your graveyard
Use Anticipate on turn 2 to find counter magic.
Do not counter Hangarback Walker or Sylvan Advocate.  You eventually can put those in check with Drowner of Hope or a planeswalker then exile them with Ulamog.
Kozilek’s Return’s flashback ability cannot be prevented by Dromoka’s Command.

Bant Humans
-4 Spell Shrivel, -1 Mage-Ring Network, -1 Ulamog, the Ceaseless Hunger -2 Jace
+2 Fiery Impulse, +1 Kozilek’s Return, +1 Deceiver of Forms, +2 Rending Volley +2 Roast
Rites Company Decks
-2 Clash of Wills, -2 Spell Shrivel, -1 Mage-Ring Network, -1 Ulamog, the Ceaseless Hunger
+2 Fiery Impulse, +1 Kozilek’s Return, +2 Roast +1 Deceiver of Forms
Orzhov Control
-4 Spatial Contortion,-1 Clash of Wills, -1 Kozilek's Return
+3 Smasher, +2 Negate, +1 Kozilek
Grixis Control
-4 Spatial Contortion, -2 Clash of Wills, -2 Hedron Archive
+3 Reality Smasher, +3 Negate, +1 Deceiver of Forms, +1 Kozilek
Red Green Ramp
-2 Spatial Contortion, -3 Kozilek’s Return, 1 of these two (-1 Ulamog, the Ceaseless Hunger, -1 Highland Lake)
+3 Negate, +3 Reality Smasher
Mono White Humans
-2 Ulamog, the Ceaseless Hunger, -4 Spell Shrivel, -1 Mage-Ring Network -1 Jace, Unraveler, -1 Clash
+3 Fiery Impulse, +1 Kozilek’s Return, +2 Roast, +1 Deceiver of Forms, +2 Rending Volley
Golgari [Including Sultai, Great Aurora and Abzan]
-2 Spatial Contortion, -1 Chandra, Flamecaller, -3 Kozilek’s Return -1 Clash of Wills
+3 Reality Smasher, +3 Negate, +1 Deceiver of Form
Izzet Eldrazi
Not sure.  I always lose this match-up since people play Reality Smasher and I do not since I find it narrow otherwise. I think your best bet is:
-4 Spatial Contortion, -3 Kozilek’s Return
+3 Negate, +3 Reality Smasher +1 Kozilek
Blue Prison
-4 Spatial Contortion, -1 Highland Lake -1 K Return
+3 Negate, +3 Smasher