With beautiful Karon Beach just a five minute walk away you might have no desire to travel any further for sand and sea but Phuket is famous for its numerous beaches and here are just a few that you may wish to try:
Kata Beach is just a twenty minute walk from Pineapple Guesthouse, more of a bay than Karon with gently shelving sands making it particularly suitable for children in high season. In September and October surfers take over here and you can spectate or participate depending upon your desire. Travel just a little further and you'll stumble across Kata Noi Beach, good for swimming.
If swimming and sunbathing's your thing, you are spoilt for choice as besides Karon, Kata and Kata Noi you can try Nai Harn, Laem Singh, Kamala or Bang Tao. Good snorkelling can be found at the smaller beaches of Ao Sane and Yanui in the south and if you want to try a more secluded beach find your way to Freedom Beach, Nui Beach or Banana Beach. For jetskis and other noisy watersports Patong's the place, though the party beach of old, Surin, has lost its famous beach clubs.
It's not worth listing all the beaches as there are so many. Find them yourselves.