I guess the fact that two of my all-time favorite series haven't been mentioned here would maybe mean I rate these series higher than is the mean.
Hourman by Tom Peyer and Rags Morales. I was so sad when this went away.
The Shadow by Andy Helfer and Bill Sinciewicz (and then later Kyle Baker). Some of the trippiest art and weirdest writing ever.
I wish I still had my copies. I'd re-read them right now.