The Avengers co-stars Scarlett Johansson (in Roland Mouret) and Jeremy Renner were among the big screen stars who gave fans a sneak peek at their upcoming movies during Disney’s D23 Expo in Anaheim, California. "What are we avenging?" Johansson jokingly asked. "We're still trying to figure it out." Click through the gallery to see Rihanna, Jennifer Garner and more stars at this weekend's hottest parties!