The popular beaches in Dubai are as follows: Jumeirah Beach - This is one of the most popular beaches in Dubai. Tourists can enjoy many water sports at the beach like water skiing, paragliding, jet skiing and much more. The beach has cafes which sell snacks, hot and cold drinks. Kite Beach - Like the name suggests this beach is popular for its kite surfers. Just as Jumeirah beach at this beach you can also do many activities. There are no eating places by the beach so its a good idea to carry your snacks and water with you. Al Mamzar Beach - This is much of a hidden beach in and again there is no shortage of activities here. Monday and Wednesdays are only for ladies and children.The beach has showers and shelters. You can also rent chalets here which are chargeable on a daily basis. Sunset Beach - This is a beach where many families and tourists visit. It is famous for taking long strolls along the sand and also its beautiful sunset view. JBR Beach - JBR Beach is the short form for Jumeirah Beach Residence and it is another popular beach to visit. This beach has a lot to offer for those interested in sports, as their is a running track. Often sporting and motor events are held at the beach. Burj Beach - Burj Beach is another popular beach which people generally visit to spend some quality time with family and friends. You would find surfers and swimmers at this beach. Water sports are also available here like banana boating, wake boarding and others.
I personally think and agree with @Deven about the popular beaches in Dubai which are Jumeirah Beach Park which is my favorite and it happens to be not free-of-charge unlike other surrounding beaches near Jumeirah but it earns you your privacy and many fantastic things and scenes/sites in store. JBR Beach, Al Mamzar Beach Park (located at the border of Dubai and Sharjah), Kite Beach (go chase the wind and kite-surf here), Umm Suqeim Beach (this is the spot for those who want to sit and stare at the undeniably striking structure that is the Burj al Arab), together with the Sunset and Burj Beaches are a must-visit if you looking for a chill-out beach spots.