There are a lot of great suggestions here and since everyone else is ignoring your pedal steel requirement, I will, too.
Asking for coutry music suggestions is like asking for classical music suggestions, you'll get everything from Satie to Wagner and that's not a lot of help in narrowing things down. Julie Miller and Billy Ray Cyrus are about as far apart as Satie and Wagner
I seem to be attracted to the music that sort of out there between genres. Lyle Lovett's an example; you're just as likely to hear a cello as twin fiddles in his arrangements.
One of Willie Nelson's most interesting is 'Teatro,' a blend of country and with the New Orleans influence of Daniel Lanois, and the above-mentioned 'Stardust' rendition of old standards (or lounge music, depending on your perspective.)
The Mavericks, Los Super Seven and Rick Trevino mix country and Latino music, which leads you to Flaco Jiminez, and you have to learn some stuff about about the European colonization of Mexico to figure out why a Tejano is playing an accordion.
You might consider Guy Clark and Townes Van Zandt as country but you'd be as likely to find them filed under folk in some record stores.
Emmylou Harris is comfortable with, and good at, all of it and there are lots of others who mix new sounds with what you'd think of as traditional country music, Lyle Lovett, Ry Cooder, Asleep at the Wheel, Dwight Yoakum (though in the case of Yoakum, it might be a stretch to call Buck Owens 'traditional' country.)
And speaking of traditional country, Iris DeMent, Nickel Creek and Gillian Welch are doing traditional but it's just another step over to Alison Krauss and Buddy and Julie Miller and a mix of styles.
You can start with The Byrds' 'Sweetheart of the Rodeo' and work your way through the Cosmic Cowboy detour, though I recommend you stop pretty quickly after you start.
An interesting sampler is 'Rhythm, Country and Blues,' though only a few of the rather strange pairings really work and they're all over the top.
So, lots to listen to.
