I follow quite a few stock models on Deviant Art and one of the best is SenshiStock who you can find here.
Recently I figured out that she has her own page where she sells stock packs. And a new item on that page is her shiny new stock cards found on this page. Here’s an image of the entry so you can find it:

They looked really good, so OF COURSE I ordered them, and I turned out to be right – they’re amazing.

To give you an idea of what they have, on one side they have a photo of the stock model, and on the other they have a 3-D with reference lines sketch of that image.
So, the photo:

And on the back of the card, the sketch:

I actually prefer the 3-D sketch side to work from, but the model side allows me to see the lighting and shading possible with this pose.

It’s an AMAZING product, and I’m really happy I ordered them. If you enjoy drawing people, I’d definitely recommend. The model is a pretty average size – not thin, not overweight, which is perfect for my drawing.
What type of references do you use for your drawing? How do you credit them? Inquiring minds want to know!