I feel like a big component of white aggro's identity is prowess or spell triggers ran in conjunction with instant speed protection effects or aggro friendly removal, the other portion being artifacts.
I've been very happy with shelter, feat, and apostle's blessing. Blessing shouldn't really be thought as a white card, however, since it also serves to fill disruption gaps in every other aggro deck, and thats the big reason to run it. Feat is nice because white usually has some minor counters sub-theme or vertical growth on DS creatures, and its a nice overlay. Shelter is also good because it helps those decks dig, which is an effect they want.
Here is another really good card for those decks