Vinyl is easy. Just add a touch of reflection and a glossy node to the material. 

Leather is about surface texture (bumps), imperfections in color, and a softer gloss, but there are so many finishes possible that no single solution will be perfect for all. Give me a photo of what you want and I can show you how to do it.

I've done very extensive work on woven cloth. Cloth is a very complex material and I've done a lot of work on that. It's not for the fainthearted. Some of my cloth materials use over 300 nodes. You'll want to check out matmatic and the Loom over at RDNA in the Poser 6 forum and the Node cult forum. Again, if you have a specific example of what you're after I'd love to help.

Denim, especially blue jeans, have all kinds of details in them. The absolute best results are achieved with photos. See this thread for examples:
www.runtimedna.com/mod/forum/messages.php

For a uniform denim material using a procedural texture (no images) see this thread and scroll down to post #45:

www.runtimedna.com/mod/forum/messages.php

You can see dozens of other cloth examples using my Loom script found in the Node Cult.

www.runtimedna.com/mod/forum/messages.php
www.runtimedna.com/mod/forum/messages.php
www.runtimedna.com/mod/forum/messages.php
www.runtimedna.com/mod/forum/messages.php
www.runtimedna.com/mod/forum/messages.php

Note that those links look the same because of how I pasted them into this silly editor but they are different.

Please do come to the Node Cult for help with cool shaders. There's a bunch of people there who love to talk about nodes.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)