Not an observation about drawing districts, but I've always been fascinated by enormous seats where the population is in one corner (the way TX-23 is enormous but most of the voters are in the San Antonio suburbs). Most of the people in MI-1 actually living in the part of the seat that's in the Lower Peninsula, even though it's also mostly rural and geographically much smaller than the Upper Peninsula, is another good wacky population-distribution observation.
I think the huge Canadian northern ridings also often have, like, most of the people in one city.
NV-4 is another good example of this.
