There are (hundreds of) thousands of excellent photos of human skin if you know where to look. If you're going for a cartoon look then that's a whole different thing. For that you pretty much need to make your own textures. Although I wouldn't even use textures, just single color materials.
I'm going for a Saint's Row 2/3 level of realism graphically. I think I've got that more or less. It looks a lot better ingame too.

I hope I can somehow smooth out the shadows though. They don't look all that good on my character or my car.