Wow, no responses yet? Then it pleases me to be the first!
Batman: The Animated Series (the 90's one, not the over-stylized new one). Great throwback art deco style (the producers called it "Dark Deco") reminiscent of the old Fleischer Superman cartoons. The style was continued for quite some time throughout the DCAU - Superman, Justice League and looked awesome.
Now it seems they're all using some kind of pseudo-anime style that I just don't dig (and I love anime - just not anime wannabe styles).