I don't think any breed is absolutely nonallergenic, but I've consistently heard that people who are allergic can tollerate Cornish Rexes. I've also spoken with one woman who was violently allergic (we're talking ER visits here) to "regular" cats but was able to live with 3 Cornish Rexes.
There's a few breeds most allergic people can tolerate such as the mentioned cornish rex. They say most people with allergies can tolerate the spynx,Siberian,Siamese, Oriental shorhairs and Devon Rex.
I forgot which month it was, but there's an article in Cat Fancy magazine about someone wanting to create a cat thats allergen free. It's pretty interesting although I don't agree with the methods used to come up with one of these.
If it is out there, somebody somewhere is allergic to it. So no, there is no cat no one is allergic to. But as mentioned before, there are some people have luck with. People say the Rex varities are good, and also Siberian cats. I don't know about the Rex cats, but Siberians have less of the protien that causes dander. If people are truly less allergic to Rexes, it would be for the same reason. Do no imagine that because a cat has less hair, it will be less allergenic. You are allergic to the dander, not the hair.
At the University of Colorado (I'm pretty sure) there is a couple starting a highly controversial experiment to try to make non-allergenic cats through gene-alteration. This is controversial for several reasons. First, they do not know if it will work. Second, they do not know how it will change the cat, healthwise and otherwise. Third, they will need to make lots and lots of new cats, which will need to be homed or killed eventually, even if the experiment does not work. Fourth, the potentially non-allergenic cats will not be available until at least 2003, and then cost between $750 and $1000.
I am qite allergic to cats. It used to take just 15 minutes in a house with cats before i was ill. I took allergy shots as my friends all had cats.
I now have two Cornish Rex. Before the breeder would let me buy my first, I spent 3and a half hours in her home, playing on the floor with her many cats. I did fine and then i was permitted to purchase a cat. She later asked me to take another retired female. I do have to be careful to keep my hands out of my eyes. It helps to bathe the cat( my former show cats are easy to bathe) or use one of the products available to reduce dander. I suggest an allergic person be sure they can return the cat if it doesn't work out.