This is a review of the beach Mar Bella (Playa de Mar Bella). You get there easily by taking the metro to 'Poble Nou' and walk straight to the beach.
A day before I went to Sitges and I think the beach of Sitges is far less fun to be at. Playa la Mar Bella is bigger (wider, more space, better sand), mixed nude & regular, very gay but you'll also see straight people going there.
After a night in the disco D-boy you'll find all the muscle marries here in the afternoon. A lot of guys of Barcelona seem to go here, especially on a Sunday when there's not much going on in Barcelona because most shops are closed.
Very nice beach, definately a recommend to go!
In Summer there is nothing better then close the weekend with a beach party. So that is what they do at the fashoinable Mar Bella Beach (east of town, metro Poble Nou).
Mixed gay/straight crowd ... but both think this is the best Barcelona has to offer.