Last year ('09) for late additions I used a blend of Sorachi Ace, Simcoe, Amarillo, and Columbus. I mostly bittered with Magnum, and those were some some tasty APAs.
This year I used Summit, Centennial and Citra for my late additions, and switched to Chinook for bittering late in the summer. I don't think I've made an APA that I really liked as well as last year's blend. Its more harsh yet lacks depth of flavor, I think it is maybe a lack of piney flavor that I'm missing. I'll be ordering up a new batch of hops for the coming year and I'll probably go back to some of the varieties I enjoyed in 09, possibly keeping Chinook as my bittering hop since my last purchase is still fairly fresh.
What are some of your favorite blends for APA's? I'm considering my options for the new year.