I like Xfx's double lifetime warranty, as well as the fact that they have customer service presence here in the forums as well as excellent customer service available in the United States.
Double lifetime warranty. I end up selling most of my hardware at some point and it's nice that the next owner can register the card without a problem.
XFX, ATI 6990 = I'm drooling! "It's even faster than the fastest video card in the world, they would know since they made that too!" I think that sums it up.