Best beaches on the North Shore?

I will be staying on the island of Oahu this summer and would like to visit one of the beautiful beaches on the North Shore. I also plan on going to the Dole Pineapple Plantation while there. Can anyone recommend some good places to visit in the North Shore or just Oahu in general? Also, if you could think of any 18+ clubs or things to do at night, that would be great! Thanks to all who answer! :)