Diablo – How are attributes allocated

Strength increases your Armor by 1 point per point.
Dexterity increases your dodge chance by 0.01%-0.1% per point.
Intelligence increases all resistances by .1 per point.

This has a number of interesting effects - most notably, because of the way Resistance works (it's functionally identical to Armor), stacking small amounts of Int on a Barbarian, Demon Hunter, or Monk can result in a dramatic survivability increase.

Resistance, like Armor, will reduce all damage you take, and, like armor, you gain substantially larger marginal benefit by increasing it when you don't have much. Since typically, a Monk (for example), will have a reasonably high Armor stat from gear and passives, and very low Int, adding just a little bit of Int via an oddly itemized piece of gear can provide a really large survivability boost - certainly more of one than trying to add Armor via Strength.

However, because everyone has a decent amount of Armor inherent in their items, increasing Strength for a similar benefit is generally not worthwhile unless you're playing a Barbarian that wants the damage boost as well, or a Wizard or Witch Doctor with a very high Resistance stat already.

Strength

• Each point increases Barbarian's damage by 1%
• Each point increases armor by 1 for every class

Vitality

• Each point increases your Life (dependent on your level, higher level=more vitality per point. See below for formulas) for every class

Life when player level < 35 = 36 + 4 × Level + 10 × Vitality

Life when player level ≥ 35 = (level - 25) × Vitality

Source

Intelligence

• Each point increases Wizard's and Witch Doctor's damage by 1%
• Each point gives .1 to all resists for every class

Dexterity

• Each Point also increases Monk's Armor by 1 with the Seize The Initiative passive unlocked at level 20.
• Each point increases Monk's and Demon Hunter's Damage by 1%

• Each point increases chance to dodge for every class

    Dex range     Dodge% per point of Dex
  
   1    - 100             0.100
  
   101  - 500             0.025
  
   501  - 1000            0.020
  
   1001 - 8000            0.010
  

Source