Hello,
does anyone know of a comprehensive shader collection, that includes a wide variety of shaders? Thanks in advance

shade-c has a tut on how to use it too

you can check the AUM too, there are lots of shaders and other goodies in there too

but it depends on what you need... corrently shade-c evo the best quality alternative, but for more simple cases its 0.91 version is also useful, e.g. I used it partially for my editor, which also offers a set of shaders. and yes, the forum and AUM-s also contain good stuff, just requires some time to find them...

Here is slin's Massive Shader Collection download link:
Shaders