Another surprising discovery today. Ecologists have long decried the destruction of rainforests due to the loss in biodiversity this represents. (Millions of unique species of plants and animals live in the rain-forests, and when they're gone, we will not be able to replace them.) Also, for all their lushness, rain-forests typically have very poor soil and fertility, so the typical burning-them-for-farms typically doesn't work out well for anyone.
Discovery News now reports another thing good for the rain-forest: it prevents malaria. Apparently, mosquitoes grow very well in puddles that form in cleared areas. The increased sunlight means more of the algae that larval mosquitoes feed upon, the lack of animals causes fewer of them to be eaten, and when they grow up, the females become disease vectors as they bite animals for their blood, which both feeds them excellently and helps them to lay more eggs. (Malaria is one of these blood-borne diseases, spreading as the mosquito first bites an infected animal, then inadvertently infects every animal she bites thereafter.)
Though I suppose this could also be nipped in the bud by draining all the little stagnant ponds in cleared areas.