Sigershaders has several undeniably good materials and base materials for more complicated setups but I would still not be too hesitant to buy. "692 Corona material presets and templates." for example is misleading since if you browse through the materials you'll notice there's a base for various material types that is been used repeatedly just changing the diffuse color and counting that as a new material. It's all good stuff and growing but I find the ethics a bit lacking when you have 30 materials under the category Stucco / Plaster and it's actually the same one just with a different hue.
