I like to use grunge or cloudy brushes and then I just do a heap of filters like blurs and anything else which I feel like using.
I would use grunge, spatter, star and abstract brushes. I would brush over stock images of anything really and play around with their blending options. The i would use filters like motion blur, gaussion blur then play around with the blending options again.
abstract brushes are my favourite.. grunge brushes are really good too.. sometimes just a stock looks good if you add effects to it and lightly go over with brushes..
something that isnt a brush, isnt a person.. something like a bridge, or a football field.. stuff like that..