I just have a lot of different stuff, pads, rhodes, acoustic instrument samples, samples from songs, mostly anything with a lot of different sounds, then I transform them into something new (it's so versatile, the UW)
no vocal samples for me (though I had: "Cold getting dumb" by Just Ice loaded once
)
I've found out the samples that I concentrate on too much are the boring ones, the more "random" and "faster" sampled samples always come out best (the one's I'm not expecting much from)