There are several beaches in Puerto Vallarta, but these are the ones that I visited:
PLAYA DEL SOL
This beach is also called "Playa de Muertas" (Dead Beach) because there used to be battles here between the Indians and sailors, which often left dead bodies on the shores. Today, the beach is the most popular one with all kinds of people from locals to tourists. Sandy and always crowded.
CONCHAS CHINAS
This beach is not really a tourist-y spot (it was rainy while we were there), but it is cool because it's got dark rocks with natural pools. You can clearly see the fish and sea plants in the water.
YELAPA
This was one of the beaches we visited on our boat cruise. It's a small town, famous for the 100 foot waterfall at the top of a big hill. At the bottom of the hill there is a beachside restaurant and a horse rental place. You can rent the horses and ride to the top of the hill, through the gorgeous, lush tropical vegetation... It takes about an hour. Once at the top, you can dine at the waterfall-side restaurant or stand in line to DIVE off the top of waterfall into the pool of water (with a natural spring) at the bottom. We opted to just grab a bite there and then take the horses back down. The beach itself is just sandy with a few rocks. It was nice to walk up and down, but nothing special (it was also gray skies while we were there).
There was also a stone beach in front of our hotel. The shore area was small, but the water was gorgeous.