Blowing my Blendswap downloads on a bunch of CC0 Cycles materials. When it comes to materials, I don't even bother looking at something unless it's CC0/public domain-- it's not worth managing license info for mats.
www.blendswap.com/blends/view/… : Good looking metals, wide enough variety, fairly easily customizable color. Good pack.
www.blendswap.com/blends/view/… : A huge pack, but without any preview. I started previewing until I saw that a material used UV coordinates when I wasn't using a UV mapped mesh and said, screw it. Bad render+preview settings in the file makes it even harder to see if there are any good mats. Missing textures. The mats I saw were nothing special. Not worth the download IMO.
www.blendswap.com/blends/view/… : Beautiful procedural leather, incl. good-looking procedural normals. Nodes setup looks messy, and you probably need to edit it (for things like scale), which might be a pain. Very worthwhile though.
www.blendswap.com/blends/view/… : A single good looking wood mat. But it uses a colored texture, which both limits recoloring and causes problems at seams. So-so download.
www.blendswap.com/blends/view/… : Doh! The first time I looked at this I did something stupid, maybe I was just looking in solid view. This is actually a very nice collection of diverse fabrics with procedural bump. Good download.
www.blendswap.com/blends/view/… : A somewhat diverse group of well-made mats: ceramic, cast-iron, car paint, two curtain fabrics, brushed metal, some other boring metals/plastics. Normals and alpha on them where appropriate. Includes a single texture, a good leather bump, but I'm not sure what uses it, since there's no leather mat; other stuff still uses UV coords. Doesn't have a billion recolored copies, which is nice. Poor preview settings in the file, single object makes it more difficult to preview. Good download.
www.blendswap.com/blends/view/… : Variety of "coated glossy" shaders that are supposed to look like plastic, metal, or ceramic, but which all look fairly ceramic to me. But it's a good ceramic, with a wide variety. Comes with preview jpgs that are nice. Nodes are intended to be edited but aren't very friendly to editing (a lot of "coated glossy group.008" kind of stuff.) Decent download.
www.blendswap.com/blends/view/… : Procedural wood, with good grain, no use of vertex UV. No normal or bump. Colors modifiable but not as easily as they should be. No clearcoat. Decent download.
www.blendswap.com/blends/view/… : Shiny hexagons. I was hoping this was from generated textures coords, but no, it's from vertex UV, so vulnerable to seam issues. Alas. Node group has problems with tangents and isn't anything interesting, but at least the included hexagonal normal map tiles well. Poor download.
www.blendswap.com/blends/view/… : Wicker chair mat using colored textures, vertex uv, and nothing special in the nodes. Would save you a minute if you want to use this exact material, but won't be useful for anything else. Poor download.
www.blendswap.com/blends/view/… : Three well-organized and not overthought shader groups: a glossy with fresnel, a metal, and a glass. All look good (but the metals at the top looked better than this metal.) All intended for customization and well-designed to that end. Includes some good textures, but the node groups themselves don't are about vertex UV. Good download.
www.blendswap.com/blends/view/… : Procedural gingham with procedural bump. The bump isn't very good. Good enough if this is exactly the mat you want, otherwise, probably not worth the download.
www.blendswap.com/blends/view/… : Very nice nacre (pearl) shader. Unfortunately doesn't preview well (needs a lot of samples before it stops looking like multichromatic noise) which makes it hard to tune, and the default settings are a little overboard. But this is a tough material to get right, that you're probably going to need only once, that's a focal point-- good download.
www.blendswap.com/blends/view/… : A collection of procedural camouflages that differ only in color. It's a simple musgrave from generated coords that makes the pattern. Overall node layout is weird and kind of dumb and difficult to expand. But if you need a CC0 camo in a hurry, hey, this is that. Decent download.
www.blendswap.com/blends/view/… : Another collection of camos that differ only by color. (Guys, we can choose colors.) Better nodes, organized, but not with English names (German? Not sure.) Don't like that the colors are managed by color ramps, which make it hard to edit. Decent download.
www.blendswap.com/blends/view/… : Aerogel material (soft edges). I downloaded this because I haven't been able to get similar looks from volumetric shaders without emission, which needs to be tuned to scene lighting since it's kind of a cheat, and I was hoping this didn't use emission-- but nope, it uses emission. Still, decent material, although there are drawbacks to it.
www.blendswap.com/blends/view/… : A well organized, better-than-default velvet shader. Velvet shaders don't bake well, and so I tried a bake test on this. Which took forever. I cancelled it half way through. I don't think it was going to bake well. But, nice velvet shader.
www.blendswap.com/blends/view/… : This is actually CC-BY but I wanted to check out the effect. It's faking volume absorption through the use of ray length. If you don't mind using CC-BY materials, these would make good shaders for candy. Even though these don't use volume, they use glass shaders, so there's probably not much of a performance improvement when using these at defaults.