Better Beacons

Iron Block:  Offensive
  Tier 1: Strenght
  Tier 2: Lower Attack Cooldown
  Tier 3: Utility Mobs + Wolfs will be stronger, and won't die¹
  Tier 4: The Beacon turns into a turret²

Gold Block: Utility
  Tier 1: Speed
  Tier 2: Jump Boost
  Tier 3: Haste
  Tier 4: +2 Increased Reach (From 5 blocks to 7)

Emerald Block: Environment
  Tier 1: It won't rain/snow in the range of the beacon, and lightning won't strike
  Tier 2: Fire won't spread
  Tier 3: Increased Growth Rate, and animals grow/breed faster (including villagers)
  Tier 4: Mobs will only spawn in light levels <= 4

Diamond Block: Defense
  Tier 1: Resistance
  Tier 2:
  Tier 3:
  Tier 4: Mob Griefing off (excluding villagers harvesting crops)

[note 1] When utility mobs reach health 0, they will enter a "defeated mode". They won't attack aggressive mobs anymore, until the player comes to them and gives them one of the appropriate item (Snow Golems: snow block, Iron Golems: iron block)
[note 2] http://i.imgur.com/DF7iPTR.jpg