If you're in Ibiza for more than a weekend without sleep in some of the world's best clubs, then you're going to want to take the ferry to neighboring Formentera.
A small island with a population of about 7,000 that really blows up around peak season, you'll be happy to have escaped the brain-numbing clubbing crowd for the welcome respite of white sand and world-class water found at Ses Illetes, which is more beautiful in that it is encroached by the ocean on two sides. Be prepared for a packed beach, though, for word is out about Ses Illetes.
For comparable conditions without the swarms of people, try out nearby Cala Conta, although it may be good to keep your plans open depending on the wind direction. It's not hard to change your beach on an island so small!