Living Lines Library has updated their site with a lot of new work, including concept art from the DreamWorks film 'Rise of the Guardians'. There, you can see a lot character concepts, as well as color keys and storyboards.
I really enjoy seeing all the different styles they could have gone with for the character Jack Frost. It seems to me like the alternate concepts would have resulted in a completely different film.
DreamWorks has also produced some really cool 'how to draw' videos, which you can find on Youtube. The videos are drawn and narrated by actual concept designers for the film. Each video depicts a different character, and is narrated by a different artist. Again, it's really wonderful to see how much variation there is in their styles, all the while maintaining the 'essence' of the character.