The sites which are filtered in Iran usually have political or unethical content such as pornography sites. In addition, some social sites such as dating and some social media are all also filtered. Look at the following for some of the most common ones:
www. facebook.com,
www.twitter.com,
www. tripadvisor.com
www.flickr.com
The typical way to access the sites is using proxy or vpn services so you’d better find one before going.