Just ran across an epic free app to make 8K res displacement maps (greeble style). It's called JSplacement. Lots of options and variety to play with so you can customize them. I think there is even a way to add your own sprites. Pretty sweet! Level up your daily renders yo. Get the app here: windmillart.net/?p=jsplacement
Also, check out David's tutorials here: eyedesyn.com/tutorials
For more free training and 150+ free models, go to thepixellab.net