Stars' Summer Lovin'

Check out the hottest celebrity romances of the season (including The O.C.'s Mischa Barton and beau Brandon Davis). By Serena Kappes with Laura J. Downey


Johansson, 19, and Leto, 32 (in New York on Aug. 7), have been spending plenty of time together of late. At a recent "Un-Birthday" party the actress threw for herself and a friend in London, a pal told PEOPLE the pair was inseparable: "She was sitting on his lap. They were kissing a lot."