Hiroyuki Imaishi, full stop. "Dead Leaves" and "Panty and Stocking with Garterbelt" are the two main works of his that I'm totally obsessed with. Not just because of their styles, but for more personal reasons as well.
I also love Tetsuhiko KIkuchi, the former go-to character designer for Treasure.
I pretty much love anything that is expressive, colorful, and dynamic.