I can contribute a few to this reference library.
Lizards and snakes below are found in the Sonoran desert (Tucson).
Lizard - unidentified species. I have another shot of him showing more close-up detail if anyone needs it.
Lizard - zebra tailed, two different individuals:
Lizard - common side-blotched, two different individuals:
Rattlesnake - western diamondback:
[I have several shots of this snake having his dirt nap; these are the two that best show his coloration and pattern; feel free to PM me if you'd like others, like from the front or rear].
Rattlesnake - Mojave:
Not the best shot, since they don't pose for photos (this is the most venomous snake in North America, and I wasn't going to risk getting closer with only a 55mm zoom lens), but it does show his pattern and coloration that could be used for a reference.
I have 2 photos of a black-tailed rattlesnake as well, but neither show his head, so I didn't include them. I'll be happy to provide the images to anyone who is interested.
Painted turtle - Mystic, CT:
Toad - unknown species, found in Grand Canyon creeks. They are about 2" in length with the pinkish iridescent skin you see in the photo. I have another photo if anyone needs it as well.
Hope someone(s) find these useful.