The International House of Pancakes has launched a new contemporary apparel Web site, www.ihopstuff.com. The new site is an early entree to a year-long celebration of IHOP’s 50th birthday. July 7 is the exact birthday of the Glendale-based operation. “Since we opened our doors 50 years ago, loyal guests have been clamoring for additional merchandise from IHOP, and now we are able to deliver apparel that features some of the phrases and graphics that IHOP has become famous for,” Carolyn O’Keefe, IHOP’s senior vice president of marketing said. The Web site will feature sweatshirts, hats and vintage T-shirts between $18 and $20. The merchandise will be available exclusively online for a limited time.