h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Located in Dubai, UAE, this is one of the warmest collection of beaches i've visited. The sea is crystal clear, and there are whole shoals of fish, as close as several metres off the beach (more exotic types around the rocks). The water is warm (especially in Summer), and is ideal for snorkelling. There are 5 beaches in all on the Al Mamza park, but i reccomend beach 4. There are changing/toilet facilities on all, voley ball nets, and adequate parking. The sea is sheltered, and so is usually fairly safe from currents, although be warned, it get's VERY hot in the Summer, up to a staggering 48 degree's C or above on a hot day. Sunscreen is a must.

My favourite beach in the UAE is the beach at Khorfakkan. Khorfakkan is in the eastern side of the UAE looking out over the Indian Ocean. It is a 50 mile stretch of virgin sand, alomost untouched, with little tourist industry. There are superb coral reefs off the coast and the breakers coming in off the Indian Ocean are excellent for wind/body surfing. There is a good 4/5 star hotel at Khorfakkan so there is somewhere nice to stay. As Madmunk says, temperatures in the UAE get very high in the Summer (too high to really enjoy being at the beach, unless well acclimatised) so it is best to go at Easter time or in late autumn.