When the Obamas recently announced they were searching for a dog to have in the White House, they noted that one of the criteria was that it would need to be hypoallergenic, since Malia is allergic to dogs. The media quickly raised the possibility of a White House poodle, since poodles are supposedly a hypoallergenic breed.
Skeptics have quickly pointed out that the idea of a hypoallergenic dog breed is a myth. Individuals dogs may produce less of the protein that causes the allergic reaction (and this protein can be found in the dander, urine, saliva, and fur of dogs). However, there is no dog breed as a whole that produces less of the protein. And if someone is very allergic to dogs, they're going to react to all dogs.
So, assuming that Malia's allergies are relatively mild and manageable, instead of focusing on certain breeds, the Obamas should test individual dogs for their compatibility with Malia. However, it is true they should avoid long-haired dogs because such dogs trap more allergens in their fur, in the same way that a shag carpet traps more allergens than a hardwood floor.
Links: Yahoo! News video
, How Stuff Works
. (Thanks, Big Gary!)