Bruce Timm is an animator, character designer and comics artist, best known for his work on Batman Adventures and the other DC Comics animated TV series. In the course of developing those shows he helped define the standards for modern television adventure/super-hero cartoons. He has also done a cool series of comic books with Paul Dini featuring Batman villains Harley Quinn and Poison Ivy. He is a frequent DC Comics cover artist.
This is a link given below is to The Bruce Timm Gallery at PopCultureShock. It includes a variety of images of varying sizes and degree of finish – from quick sketches to fully rendered comic covers.