If you are gonna get Gram Parsons, get the Flying Burrito Brothers stuff too. Also the International Submarine Band had some righteous songs.
For more Honky Tonkey stuff, I really like Wayne "The Train" Hancock and Hank Williams III. Both of them have a ridiculous amount of twang, but they make really good records if you can handle that.
John Prine is great, funnier than a lot of country, but his songs are really heartfelt and often quite touching.
Gillian Welch is great, she's more Folk/Bluegrass than straight country, but definitely look into her, she has a beautiful voice.
For older stuff, pretty much anything released by
Acuff-Rose will be good songs. I happen to really like Roy Acuff as a musician, but when you get far enough back a lot of the songs are about Jesus. If you can't handle that you could be in trouble. If you can handle that, The Louvin Brothers are amazing. So is Roy Acuff, and the Carter Family. I also have a soft spot for Waylon Jennings. Charlie Louvin, the surviving half of the Louvin Bro's put out a record this year that's amazing.
For women, Loretta Lynn is obvious. Get Coal Miners Daughter, and work from there, but don't overlook Van Lear Rose. It's newer, but damn its a good record. Also good are her duet albums with Conway Twitty. If you ever played GTA San Andreas and heard that song about a louisiana woman and a mississippi man? That's them. Melba Montgomery is pretty amazing as well, and so is Patsy Cline, shit the haters.
Ummm. Alt country is really good too, but that's for another day.