Here are some drawings from the developement of the Tanngrisnir wild goats. These guys were designed around the idea they'd be prime prey for dragons. As a requirement, they're pretty huge.
And here's a quick creature concept based on a thumbnail sketch by Mike Corriero.
And last but not least, some developement sketches for sapient dragons. Trying to come up with head shapes that look intelligent and maybe even a bit alien, while still retaining classic dragon features.