In the more rock than country category, I like:
Drive-by-Truckers
Slobberbone
Jupiter Coyote
Jolene
Southern Culture on the Skids
Marshall Tucker
Green on Red
Futurebirds
You guys have already mentioned many of the tight harmony, pedal steel acts like the Byrds and New Riders. I would throw in some of the Grateful Dead stuff. My list is more difficult to categorize. My list are more rock acts with country overtones. At any given moment, they might include an electric fiddle, pedal steel, or banjo in the mix with electric guitars. The common denominator of course is that they all sing about loose women, drinkin’ whiskey, and trailer parks.