Benji Madden & Cameron Diaz PDA -- Couple Heats Up Atlantic Ocean

Cameron Diaz and rocker Benji Madden frolicked around on the beach in Florida this holiday weekend, canoodling in the ocean for all the world to see.

Our photogs spotted the new couple at LAX last week as they departed for their vacay together ... a sure sign things are getting serious between them. Or she's just finding a creative way to push her new movie "Sex Tape."