World of Warcraft, Diablo 3 and Guild Wars 2 blocked in Iran.

You can still play from Iran by using a proxy!

Because the US has imposed trade restrictions and economic sanctions on the Islamic Republic, most American companies aren't allowed to do business in the country. By selling games and subscriptions to Iranian residents online, Blizzard had been doing business in Iran, and apparently that had to stop. That also means that Iranian players can't get refunds for pre-orders (like MoP, GW2) or for subscription time. The Iranian government also decided to ban most games from their country making the political dispute between the two countries stop gamers from being together, loving, chatting and slaughtering each other in thousands of fun ways.
This is from the Iranian government:

1. 
   
2. Promotion of superstition and mythology.
3. Promotion of violence due to too much violence.
4. Abolishing the deformation in sin.
5. Demonstration of inappropriate clothing and slutty outfits for female avatars.

This is Blizzard's side:

What we can tell you is that United States trade restrictions and economic sanction laws prohibit Blizzard from doing business with residents of certain nations, including Iran. Several of you have seen and cited the text in the Terms of Use which relates to these government-imposed sanctions. This week, Blizzard tightened up its procedures to ensure compliance with these laws, and players connecting from the affected nations are restricted from access to Blizzard games and services.
This also prevents us from providing any refunds, credits, transfers, or other service options to accounts in these countries. We apologize for any inconvenience this causes and will happily lift these restrictions as soon as US law allows.

BBC article.

Guild Wars 2 and other games also seem to be affected by the ban.