Country code: +98
Basic business directory for Iran with almost 18,000 entries. In English and Persian (Farsi). Requires free registration to get search results but you can see how many results are available before doing so. You just need to register to get the full information such as address and telephone number.
Yellow Pages for Iran from Telecommunications Company of Tehran. The site is only in Persian - the box on the left is detailed help (i.e. put as much info in you can about the business). The box on the right takes you to the search info. The first input box is the State, the second is the City (you get drop down options but again, these are in Persian). The third input box is the name. You really need to know Persian to get results but if you do, it's a useful resource.
It's sometimes a bit unreliable - if it doesn't load first time, keep clicking reload.