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

SCARLETT JOHANSSON & JARED LETO

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."