Largo João Soldado
This hostel, called White Sand, is really the best you can get by the beach.
If you like surfing and bodyboarding, this is the place for you to break some waves and get a cool tan (being careful not to get burnt, of course).
You can get to the beaches of Santa Cruz and Ericeira in the blink of an eye, and the nights should be full of fun, since the place is full of bars and discos.
Start making plans for a great holiday!