Gothamcitypizzeria.com
The site
Gothamcitypizzeria.com is the website for Gotham City Pizzeria, and was found on June 16th.
Clues from Joker's cellphone image pieces sent on June 13th, it is implied that a Dominoes commercial or promotion will air on June 16th, which will probably be the "Special Promotion" mentioned on Gothamcitpizzeria.com.