Check out these translated images from the official guidebook for Shadow of the Colossus. There's a bunch of concept art and character pages at GlitterBerri to enjoy.
I really dug checking out the sketches for the unused Colossi. There's some that look like they'd be quite a challenge in the mix. The fish you'd have to jab in the water in a certain spot would have had me screaming at my television if they would have used it. The monkey one that hangs from the ceiling would have also been difficult to defeat. The worst is the one they nicknamed Devil. You'll see in the translated text that he would have been evil.
If you are as big of a fan as I am of this game, these sketches and other scans are definitely worth checking out.